promote function parameters to i64 when integer-eligible

[cs01]

Summary

• Numeric function params (like lo, hi in quicksort) are now promoted to i64 when integer analysis determines they're only used in integer contexts
• Eliminates sitofp i64→double + fcmp conversions on every loop iteration, replacing them with pure icmp i64 comparisons
• Extends the existing local variable i64 optimization (PR optimize bounds checks: unsigned compare + noreturn #475) to function parameters

Test plan

• New test fixture tests/fixtures/optimization/param-i64-promotion.ts (quicksort)
• All existing tests pass
• Self-hosting verification passes

[github-actions]

Benchmark Results (Linux x86-64)

Benchmark	C	ChadScript	Go	Node	Bun	Place
Binary Trees	1.267s	1.647s	3.004s	1.516s	1.215s	#4
Cold Start	0.6ms	0.6ms	1.3ms	21.8ms	7.6ms	🥇
Fibonacci	0.725s	1.424s	1.429s	2.842s	1.837s	🥈
File I/O	0.088s	0.089s	0.088s	0.315s	0.204s	🥉
JSON Parse/Stringify	0.004s	0.005s	0.016s	0.015s	0.007s	🥈
Matrix Multiply	0.373s	0.648s	0.448s	0.413s	0.444s	#5
Monte Carlo Pi	0.400s	0.398s	0.405s	1.474s	6.428s	🥇
N-Body Simulation	1.453s	1.852s	1.964s	2.296s	2.817s	🥈
Quicksort	0.170s	0.202s	0.184s	0.249s	0.205s	🥉
SQLite	0.314s	0.374s	—	0.437s	0.371s	🥉
Sieve of Eratosthenes	0.027s	0.038s	0.033s	0.054s	0.049s	🥉
String Manipulation	0.008s	0.039s	0.017s	0.037s	0.028s	#5