Add annotate_snippets for better parsing errors (#477)

Adds nicer errors for Podlang code, using the `annotate_snippets` crate, the same crate used by the Rust compiler to generate contextual errors. This prints a short snippet of the code containing the error within the error message, highlighting the part that needs to be fixed.

It also includes a change to the `load_module` function, changing a `Vec` function argument to a slice.

src/frontend/mod.rs

@@ -1381,7 +1381,7 @@ pub mod tests {
             Equal(b, 5)
         )
         "#;
-        let module = load_module(input, "test", &params, vec![]).unwrap();
+        let module = load_module(input, "test", &params, &[]).unwrap();
         let batch = module.batch.clone();
         let pred_test = batch.predicate_ref_by_name("Test").unwrap();
 
@@ -1430,7 +1430,7 @@ pub mod tests {
             c(6, 3)
         )
         "#;
-        let module = load_module(input, "test", &params, vec![]).unwrap();
+        let module = load_module(input, "test", &params, &[]).unwrap();
         let batch = module.batch.clone();
         let pred_test = batch.predicate_ref_by_name("Test").unwrap();
 
@@ -1452,7 +1452,7 @@ pub mod tests {
             c(6, 3)
         )
         "#;
-        let module = load_module(input, "test", &params, vec![]).unwrap();
+        let module = load_module(input, "test", &params, &[]).unwrap();
         let batch = module.batch.clone();
         let pred_test = batch.predicate_ref_by_name("Test").unwrap();
 
@@ -1491,7 +1491,7 @@ pub mod tests {
         "#;
 
         // Parse and batch the predicate (this handles splitting internally)
-        let module = load_module(input, "test", &params, vec![])?;
+        let module = load_module(input, "test", &params, &[])?;
 
         // Verify it was split
         assert!(module.split_chains.contains_key("large_pred"));

src/frontend/multi_pod/mod.rs

@@ -763,7 +763,7 @@ mod tests {
             "#,
             "test",
             &params,
-            vec![],
+            &[],
         )
         .expect("load module");
         let batch = &module.batch;
@@ -1492,7 +1492,7 @@ mod tests {
             "#,
             "test",
             &params,
-            vec![],
+            &[],
         )
         .expect("load module");
         let batch = &module.batch;
@@ -1621,7 +1621,7 @@ mod tests {
             "#,
             "test",
             &params,
-            vec![],
+            &[],
         )
         .expect("load module");
         let batch = &module.batch;