auto-rebuild stale native compiler in test runner

[cs01]

Summary

• Fixes mysterious test failures after source changes by detecting when .build/chad is older than dist/ and auto-rebuilding it
• Previously the test runner only checked if .build/chad exists, not whether it's current — a stale native compiler silently produces wrong codegen, causing tests to fail with confusing errors (wrong truthiness, SIGSEGVs, missing features)

Test plan

• npm run verify:quick passes
• Verified: when dist/ is newer than .build/chad, test runner prints "Native compiler is stale, rebuilding" and rebuilds before running tests

[github-actions]

Benchmark Results (Linux x86-64)

Benchmark	C	ChadScript	Go	Node	Bun	Place
Binary Trees	1.343s	1.222s	2.767s	1.180s	0.985s	🥉
Cold Start	1.4ms	0.8ms	1.2ms	23.8ms	8.8ms	🥇
Fibonacci	0.814s	1.534s	1.563s	3.151s	1.941s	🥈
File I/O	0.115s	0.090s	0.086s	0.211s	0.183s	🥈
JSON Parse/Stringify	0.004s	0.005s	0.018s	0.015s	0.007s	🥈
Matrix Multiply	0.449s	0.694s	0.613s	0.367s	0.347s	#5
Monte Carlo Pi	0.389s	0.410s	0.404s	2.248s	6.026s	🥉
N-Body Simulation	1.678s	2.118s	2.203s	2.387s	3.267s	🥈
Quicksort	0.215s	0.245s	0.213s	0.261s	0.226s	#4
SQLite	0.356s	0.400s	—	0.441s	0.403s	🥈
Sieve of Eratosthenes	0.015s	0.028s	0.020s	0.039s	0.036s	🥉
String Manipulation	0.008s	0.045s	0.016s	0.035s	0.027s	#5

CLI Tool Benchmarks

Benchmark	ChadScript	grep	node	xxd	Place
Hex Dump	0.429s	—	1.035s	0.128s	🥈
Recursive Grep	0.019s	0.009s	0.094s	—	🥈