[codex] Fix object numeric index assignment

[andrewtdiz]

Summary

• canonicalize property keys in the ordinary PutValue target setter before writing object fields
• fixes numeric computed assignment on ordinary objects, e.g. obj[1] = value creating/updating property "1"
• adds a focused c262 regression for creating and overwriting numeric object keys

Scan notes

Initial baseline after building only the Perry CLI was infrastructure noise: scripts/test262_focused_report.py --root vendor/test262 --dir language/expressions --max 500 --sample-cap 1000000 --timeout 20 reported 285 compile-fail, all Error: Could not find libperry_runtime.a.

After building static archives with cargo build --release -p perry-runtime -p perry-stdlib, the same baseline was real parity signal: 500 judged, 482 pass, 18 runtime-fail, 0 compile-fail, 0 skip.

The fixed failures were:

• language/expressions/assignment/S8.12.5_A1.js: obj[1] = ... did not create property "1"
• language/expressions/assignment/S8.12.5_A2.js: obj[1] = ... did not overwrite existing property "1"

Post-fix language/expressions --max 500: 500 judged, 484 pass, 16 runtime-fail, 0 compile-fail, 0 skip.

Focused assignment follow-up: scripts/test262_focused_report.py --root vendor/test262 --dir language/expressions/assignment --max 500 --sample-cap 1000000 --timeout 20 --skip-vendor --skip-build reported 207 judged, 196 pass, 11 runtime-fail, 0 compile-fail, 0 skip; S8.12.5_A1/A2 no longer appear in the problem TSV.

Validation

• cargo build --release -p perry-runtime -p perry
• cargo fmt --package perry-runtime --check
• tests/test_c262_object_numeric_index_assignment.sh
• scripts/test262_focused_report.py --root vendor/test262 --dir language/expressions/assignment --max 500 --sample-cap 1000000 --timeout 20 --skip-vendor --skip-build
• scripts/test262_focused_report.py --root vendor/test262 --dir language/expressions --max 500 --sample-cap 1000000 --timeout 20 --skip-vendor --skip-build