fix(runtime): a built-in callee receives the primitive `this`, not a ToObject wrapper (re-land `32f150b22` from #9800)

[proggeramlug]

Problem

call_primitive_closure_value (crates/perry-runtime/src/object/native_call_method.rs ~L317) still wraps the receiver with js_object_coerce for every non-strict callee, including built-in functions. Per spec, built-ins receive the primitive this unwrapped. The closed draft #9800 fixed this in commit 32f150b22 (the native_call_method.rs change plus its test). Its gated A/B showed byte-identical output on 51 cases (thunks unwrap anyway), so this is spec alignment plus a cost bound: no per-call wrapper allocation if a built-in without a native arm is ever reached.

Fix

Re-apply only 32f150b22's change on current main (git show 32f150b22; the branch was perf/builtin-callee-no-toobject), using builtin_closure_length / builtin detection as it exists on main now. Don't carry #9800's older stacked commits.

Verify

• The ported test goes red without the fix (sabotage).
• The gap suite shows no regressions against a pristine main build (A/B the named tests if anything moves).

Rules for the PR (repo conventions)

• Code + tests + a changelog.d/<PR>-<slug>.md fragment. No version bump (don't touch [workspace.package].version, the CLAUDE.md version line, or Cargo.lock versions).
• Every new regression test must be sabotage-checked: revert the fix, confirm the test goes red, restore. Say so in the PR body.
• perry-runtime tests must run with RUST_TEST_THREADS=1. Build -p perry -p perry-runtime-static -p perry-stdlib-static together (the .a archives come from the -static wrappers).
• Run scripts/run_lint_gates.sh (or at least cargo fmt --all -- --check, scripts/check_file_size.sh, python3 scripts/raw_handle_debt.py, python3 scripts/addr_class_inventory.py, python3 scripts/gc_runtime_root_holders.py, python3 scripts/gc_rekeyed_key_tables.py).
• Self-contained: no private bundle or special host needed. A normal Linux or macOS dev box is enough.

Filed from the 2026-09 side-table / RSS audit; line numbers are against main e379a7a and may drift.