Add c262 rest-param eval regression coverage

[andrewtdiz]

Summary

• add focused coverage for Test262 language/expressions/arrow-function/scope-param-rest-elem-var-close.js
• pins the sloppy arrow rest-parameter destructuring + direct eval var binding case where both parameter-created and body-created closures must see the eval-introduced binding

Notes

• The exact Test262 target already passes on current origin/main; no implementation change was needed.
• A broader tests/test_c262_arrow_function_parity.sh verification was timeboxed after hanging in Perry compile and was terminated.

Verification

• cargo build --release -p perry -p perry-runtime -p perry-stdlib
• tests/test_c262_arrow_env_parity.sh
• one-file Test262 run for language/expressions/arrow-function/scope-param-rest-elem-var-close.js via scripts/test262_subset.py with absolute --perry-bin
• cargo test -p perry-hir --test c262_parity

Timeboxed / blocked

• tests/test_c262_arrow_function_parity.sh hung for ~4m34s inside target/release/perry compile --no-cache .../c262_arrow_parity.ts; process was terminated.