fix(math): implement Math.f16round

[andrewtdiz]

Summary

• add Math.f16round HIR lowering, codegen runtime declaration, and binary16 ties-to-even runtime helper
• expose callable Math.f16round / globalThis.Math.f16round values for property reads and alias calls
• add focused Node parity coverage for signed zero, NaN/infinities, subnormals, overflow, ties-to-even, and first-class reads

Closes #2898.

Validation

• PATH="/root/.npm/_npx/8758e404b5eed2f3/node_modules/.bin:$PATH" node --experimental-strip-types test-parity/node-suite/globals/math-f16round.ts
• pre-fix: ./run_parity_tests.sh --suite node-suite --module globals --filter math-f16round -> test-parity/reports/parity_report_20260530_033415.json (0 pass / 1 fail)
• post-fix: env RUSTC_WRAPPER= PATH="/root/.npm/_npx/8758e404b5eed2f3/node_modules/.bin:$PATH" ./run_parity_tests.sh --suite node-suite --module globals --filter math-f16round -> test-parity/reports/parity_report_20260530_035246.json (1 pass / 0 fail)
• env RUSTC_WRAPPER= cargo check -p perry-hir -p perry-codegen -p perry-runtime
• cargo fmt --all -- --check
• git diff --check HEAD~1..HEAD
• ./scripts/check_file_size.sh