fix: eliminate oob array access in function parameter counting

[cs01]

Summary

• The compiler used while (arr[idx]) to count function parameters, which accesses index 0 of an empty array when a function has no parameters. In JavaScript this silently returns undefined, but with runtime bounds checking enabled this becomes a crash.
• Replaced with direct .length check — simpler and correct for all cases.

What this means for users

Previously, enabling full bounds checking (for string/object arrays) would cause the compiler itself to crash when compiling any code containing parameterless functions. This fix eliminates one of the compiler's own out-of-bounds array accesses, bringing us closer to enabling bounds checking across all array types.

Test plan

• All 451 compiler tests pass
• Self-hosting Stage 0 + Stage 1 pass
• Verified parameterless function compilation works with bounds checking enabled

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