[codex] Preserve lexical new.target for arrows

[andrewtdiz]

Summary

• Route Expr::NewTarget through the stack-aware lowerer so arrow closures can read captured lexical new.target values.
• Propagate captures_new_target into synthesized async step closures, including awaited async arrows.
• Add a Node parity fixture for sync arrows, async arrows, awaited async arrows, and ordinary function new.target behavior.

Addresses the async/arrow new.target portion of #3568.

Validation

• npm exec --package=node@25 -- bash -lc 'node --version; ./run_parity_tests.sh --suite node-suite --module globals --filter arrow-newtarget-capture' (Node v25.9.0, 1 pass / 0 fail)
• cargo fmt --all -- --check
• git diff --check origin/main..HEAD
• ./scripts/check_file_size.sh
• CARGO_TARGET_DIR=/root/perry-worktrees/perry-generator-prototype-identity/target cargo check -p perry-codegen -p perry-transform