refactor(type-inference): memoize resolveExpressionTypeRich at the boundary

[cs01]

What changed for users

Compiler now caches type-resolution results per AST expression node. Today this is a wash (existing call sites don't repeat-query), but it unblocks the upcoming TypedAST annotator pass — which previously hung stage 2 self-compile because eager use of the unmemoized resolver was O(N^2).

Details

• Added parallel-array memoization in TypeInference.resolveExpressionTypeRich, keyed by AST expression reference identity. Chose parallel arrays over Map<object, ResolvedType> because native ChadScript's Map doesn't support object keys (a minimal repro segfaults). The previously-dormant LLVMGenerator.typeCache (PR feat(codegen): phase E substrate — ctx.typeOf() type cache #540) had this same latent bug; consolidated it away.
• Cached only for context-independent expression shapes (literals, new, array/map/set, object). Skipped for variable/member_access/index_access/call/method_call because those resolve through the symbol table, which is refined mid-codegen by variable-allocator and friends — caching them could freeze an early, less-specific answer.
• LLVMGenerator.typeOf() now delegates to the inner cache, removing the duplicate Map.

Test plan

• npm run verify (full, including stage 2 self-host) green locally
• npm run format:check clean
• Cache validated via CHAD_DEBUG_RESOLVER_CACHE instrumentation during development (removed before commit)

[github-actions]

Benchmark Results (Linux x86-64)

Benchmark	C	ChadScript	Go	Node	Place
Binary Trees	1.321s	1.055s	2.099s	1.048s	🥈
Cold Start	0.8ms	0.7ms	1.0ms	24.6ms	🥇
Fibonacci	0.705s	0.706s	1.341s	2.607s	🥈
File I/O	0.075s	0.080s	0.074s	0.155s	🥉
JSON Parse/Stringify	0.003s	0.005s	0.013s	0.013s	🥈
Matrix Multiply	0.379s	0.384s	0.681s	0.330s	🥉
Monte Carlo Pi	0.341s	0.348s	0.355s	2.011s	🥈
N-Body Simulation	1.384s	1.754s	1.773s	1.851s	🥈
Quicksort	0.191s	0.218s	0.188s	0.230s	🥉
SQLite	0.253s	0.263s	—	0.330s	🥈
Sieve of Eratosthenes	0.011s	0.021s	0.016s	0.033s	🥉
String Manipulation	0.007s	0.014s	0.013s	0.030s	🥉

CLI Tool Benchmarks

Benchmark	ChadScript	grep	node	xxd	Place
Hex Dump	0.472s	—	0.822s	0.107s	🥈
Recursive Grep	0.018s	0.010s	0.084s	—	🥈