Split Params into base and developer-defined (#458)

I thought it would be nice to have a Predicate for the typed value so that the developer can work with predicates as values comfortably.  Then I noticed that hashing a predicate required `Params` which would have been annoying for converting a `TypedValue::Predicate` to `RawValue` and this led to a small refactor over how `Params` work.

We already had some fields in the `Params` struct that determine compatibility between encoded data.  They can be seen as determining a kind of ABI compatibility.  In general it's better if those parameters don't change so that different circuit configurations can still verify proofs from each other.  So I decided to force those parameters to be constant in the code base and not allow the user of our library to change them.  Many field element serialization/deserialization functions in our code depended on those parameters, and since now they are constant many functions get rid of the `Params` argument, which simplifies the code.  This includes the serialization of a `Predicate` which was required to calculate its hash.

src/lang/frontend_ast_split.rs

@@ -76,18 +76,15 @@ struct WildcardUsage {
 }
 
 /// Early validation: Check if predicate is fundamentally splittable
-pub fn validate_predicate_is_splittable(
-    pred: &CustomPredicateDef,
-    params: &Params,
-) -> Result<(), SplittingError> {
+pub fn validate_predicate_is_splittable(pred: &CustomPredicateDef) -> Result<(), SplittingError> {
     let public_args = pred.args.public_args.len();
 
     // Check: public args must fit in operation arg limit
-    if public_args > params.max_statement_args {
+    if public_args > Params::max_statement_args() {
         return Err(SplittingError::TooManyPublicArgs {
             predicate: pred.name.name.clone(),
             count: public_args,
-            max_allowed: params.max_statement_args,
+            max_allowed: Params::max_statement_args(),
             message: "Public arguments exceed max operation args - cannot call this predicate"
                 .to_string(),
         });
@@ -102,10 +99,10 @@ pub fn split_predicate_if_needed(
     params: &Params,
 ) -> Result<SplitResult, SplittingError> {
     // Early validation
-    validate_predicate_is_splittable(&pred, params)?;
+    validate_predicate_is_splittable(&pred)?;
 
     // If within limits, no splitting needed
-    if pred.statements.len() <= params.max_custom_predicate_arity {
+    if pred.statements.len() <= Params::max_custom_predicate_arity() {
         return Ok(SplitResult {
             predicates: vec![pred],
             chain_info: None,
@@ -173,12 +170,11 @@ struct OrderingResult {
 fn order_constraints_optimally(
     statements: Vec<StatementTmpl>,
     _usage: &HashMap<String, WildcardUsage>,
-    params: &Params,
 ) -> OrderingResult {
     let n = statements.len();
 
     // If no splitting needed, preserve original order (identity mapping)
-    if n <= params.max_custom_predicate_arity {
+    if n <= Params::max_custom_predicate_arity() {
         return OrderingResult {
             statements,
             reorder_map: (0..n).collect(),
@@ -191,13 +187,8 @@ fn order_constraints_optimally(
     let mut active_wildcards: HashSet<String> = HashSet::new();
 
     while !remaining.is_empty() {
-        let best_idx = find_best_next_statement(
-            &statements,
-            &remaining,
-            &active_wildcards,
-            ordered.len(),
-            params,
-        );
+        let best_idx =
+            find_best_next_statement(&statements, &remaining, &active_wildcards, ordered.len());
 
         remaining.remove(&best_idx);
         let stmt = &statements[best_idx];
@@ -268,10 +259,9 @@ fn find_best_next_statement(
     remaining: &HashSet<usize>,
     active_wildcards: &HashSet<String>,
     ordered_count: usize,
-    params: &Params,
 ) -> usize {
     // Calculate distance to next split point
-    let bucket_size = params.max_custom_predicate_arity - 1; // Reserve slot for chain call
+    let bucket_size = Params::max_custom_predicate_arity() - 1; // Reserve slot for chain call
     let distance_to_split = bucket_size - (ordered_count % bucket_size);
     let approaching_split = distance_to_split <= 2;
 
@@ -432,7 +422,7 @@ fn split_into_chain(
     let usage = analyze_wildcards(&pred.statements);
     let real_statement_count = pred.statements.len();
 
-    let ordering_result = order_constraints_optimally(pred.statements, &usage, params);
+    let ordering_result = order_constraints_optimally(pred.statements, &usage);
     let ordered_statements = ordering_result.statements;
     let reorder_map = ordering_result.reorder_map;
 
@@ -449,12 +439,12 @@ fn split_into_chain(
 
     while pos < ordered_statements.len() {
         let remaining = ordered_statements.len() - pos;
-        let is_last = remaining <= params.max_custom_predicate_arity;
+        let is_last = remaining <= Params::max_custom_predicate_arity();
 
         let bucket_size = if is_last {
             remaining // Last predicate uses all remaining
         } else {
-            params.max_custom_predicate_arity - 1 // Reserve slot for chain call
+            Params::max_custom_predicate_arity() - 1 // Reserve slot for chain call
         };
 
         let end = pos + bucket_size;
@@ -475,7 +465,7 @@ fn split_into_chain(
             .cloned()
             .collect();
         let total_public = incoming_public.len() + new_promotions.len();
-        if total_public > params.max_statement_args {
+        if total_public > Params::max_statement_args() {
             let context = crate::lang::error::SplitContext {
                 split_index: chain_links.len(),
                 statement_range: (pos, end),
@@ -490,7 +480,7 @@ fn split_into_chain(
             return Err(SplittingError::TooManyPublicArgsAtSplit {
                 predicate: original_name.clone(),
                 context: Box::new(context),
-                max_allowed: params.max_statement_args,
+                max_allowed: Params::max_statement_args(),
                 suggestion: suggestion.map(Box::new),
             });
         }
@@ -688,10 +678,10 @@ fn generate_chain_predicates(
 fn validate_chain(chain: &[CustomPredicateDef], params: &Params) -> Result<(), SplittingError> {
     for pred in chain {
         // Each predicate should have ≤ max_statements
-        assert!(pred.statements.len() <= params.max_custom_predicate_arity);
+        assert!(pred.statements.len() <= Params::max_custom_predicate_arity());
 
         // Public args should fit
-        assert!(pred.args.public_args.len() <= params.max_statement_args);
+        assert!(pred.args.public_args.len() <= Params::max_statement_args());
 
         // Total args should fit
         let total =
@@ -729,9 +719,8 @@ mod tests {
         "#;
 
         let pred = parse_predicate(input);
-        let params = Params::default();
 
-        assert!(validate_predicate_is_splittable(&pred, &params).is_ok());
+        assert!(validate_predicate_is_splittable(&pred).is_ok());
     }
 
     #[test]
@@ -743,9 +732,8 @@ mod tests {
         "#;
 
         let pred = parse_predicate(input);
-        let params = Params::default(); // max_statement_args = 5
 
-        let result = validate_predicate_is_splittable(&pred, &params);
+        let result = validate_predicate_is_splittable(&pred);
         assert!(matches!(
             result,
             Err(SplittingError::TooManyPublicArgs { .. })