Re-implement merkletree with persistent storage (key-value db) (#487)

* refactor merkletree to work with disk keyvalue database (wip)

* various fixes post reimplementation; pending delete leaf

* add delete operation case for the new in db tree approach

* polish tree update & delete; everything works (pending polishing)

* polish panics into errs, prints, etc

* Implement iterator

* Lint

* fix case no-siblings

* case delete with semi-empty branch

* polishing

* starting to add rocksdb & heeddb for the DB & Txn traits

* Satisfy the borrow checker

* abstract merkletree tests to use the various available DBs

* update store_node interface (rm hash input), rm heed.rs

* polishing

* typos

* Ditch transactions

* add feature for rocksdb, return errs at new_with_db, remove empty leaf case in Leaf::new

* intermediate instead of leaf in empty node when deleting leaf

---------

Co-authored-by: Ahmad <root@ahmadafuni.com>

Cargo.toml

@@ -48,6 +48,7 @@ good_lp = { version = "1.8", default-features = false, features = [
   "scip_bundled",
 ] }
 annotate-snippets = "0.11"
+rocksdb = { version = "0.24.0", optional = true } # keyvalue database for merkletree
 
 # Uncomment for debugging with https://github.com/ed255/plonky2/ at branch `feat/debug`.  The repo directory needs to be checked out next to the pod2 repo directory.
 # [patch."https://github.com/0xPARC/plonky2"]
@@ -57,12 +58,13 @@ annotate-snippets = "0.11"
 pretty_assertions = "1.4.1"
 # Used only for testing JSON Schema generation and validation.
 jsonschema = "0.30.0"
+tempfile = "3"
 
 [build-dependencies]
 vergen-gitcl = { version = "1.0.0", features = ["build"] }
 
 [features]
-default = ["backend_plonky2", "zk", "mem_cache"]
+default = ["backend_plonky2", "zk", "mem_cache", "db_rocksdb"]
 backend_plonky2 = ["plonky2"]
 zk = []
 metrics = []
@@ -70,6 +72,7 @@ time = []
 examples = []
 disk_cache = ["directories", "minicbor-serde"]
 mem_cache = []
+db_rocksdb = ["rocksdb"]
 
 # Uncomment in order to enable debug information in the release builds.  This allows getting panic backtraces with a performance similar to regular release.
 # [profile.release]