perf(wasm-privacy-coin): JIT-compile WASM + cache module/pool instances

[OttoAllmendinger]

Summary

The shielded merkle tree test suite that consumes this package (MerkleTreeServiceTest, MerkleTreePruningTest, MerkleTreeEndToEndTest) was spending ~452s — almost entirely in WASM module setup, not actual tree operations. This PR makes those tests ~41x faster (452s → 10.9s) with three layers of optimization in wasm-privacy-coin.

Root cause

WasmBridge re-parsed the 466 KB privacy_coin.wasm binary and re-instantiated a fresh Chicory Instance on every ShieldedMerkleTree creation (~14s per cycle). Chicory 1.1.1 was interpreter-only, so even after caching, interpreted WASM execution dominated the remainder.

Changes

1. Module caching (WasmBridge.java) — the parsed WasmModule is cached in a static volatile field (immutable, safely shared across threads). Only the first WasmBridge() pays the parse cost.

2. Instance pooling (WasmBridge.java) — a ConcurrentLinkedDeque<Instance> reuses Chicory Instances. On close(), drop_tree drops the in-WASM tree and the Instance returns to the pool. The next WasmBridge() borrows it; from_frontier/from_state re-initializes the tree state in the existing linear memory. Failed init uses discard() to avoid polluting the pool with a dirty Instance.

3. JIT compiler (pom.xml + WasmBridge.java) — upgraded Chicory 1.1.1 → 1.7.5 and added the compiler module. MachineFactoryCompiler.compile(module) JIT-compiles all WASM functions to JVM bytecode once per JVM; the resulting Machine replaces the interpreter, giving native-speed execution that the JVM C2 JIT further optimizes.

ShieldedMerkleTree.close() now delegates to WasmBridge.close() (which drops the tree + pools the instance), and create() uses discard() on init failure.

Results (downstream shielded merkle tree test suite)

Test class	Before	After	Speedup
MerkleTreeServiceTest (15 tests)	213s	2.96s	72x
MerkleTreePruningTest (3 tests)	194s	3.38s	57x
MerkleTreeEndToEndTest (2 tests)	45s	4.57s	10x
Total	452s	10.9s	41x

Verification

• All 41 wasm-privacy-coin tests pass.
• The downstream consumer's merkle tree tests pass.
• The Chicory version bump (1.1.1 → 1.7.5) is a breaking change for any consumer still on 1.1.1.

Refs: T1-3728

[linear-code]

T1-3728