test(codegen): loop_safepoint_purity rejects current numeric-loop poll policy #8263

Current main and PR #8208 emit guarded js_gc_loop_safepoint calls in the numeric counted-loop fixture, while proven_numeric_counted_loop_emits_no_back_edge_poll still requires zero polls. The generated IR contains no #8208 release operation; #8208 only adds exhaustive ReleaseBoxes match arms in loops.rs, so it cannot affect this fixture. This became visible when #8208 classified its previously-unmapped release_boxes_lowering integration suite and e2e-scoped finally advanced past the scope check into the mapped codegen suites. Reconcile the test with the current moving-GC poll policy, or restore the intended purity proof. Until fixed, the per-test self-invalidating SUITE_EXCLUSIONS entry should name this issue.