Remove unused function warnings

[TheHypnoo]

Summary

• Removes unused helper functions and compatibility wrappers that no longer have call sites across HIR lowering, codegen, runtime, extensions, stdlib, and publish code.
• Restricts monomorphization constraint helpers to module-private visibility instead of exposing private implementation types through a wider API.
• Keeps test-only helpers available behind #[cfg(test)] where the only remaining users are unit tests.

Removed as clearly unused

• Old native-instance rewrite helpers in perry-hir::js_transform; the active class-field rewrite path now handles this behavior.
• Wrapper helpers such as fresh_global, type extraction aliases, unused tarball/error/fetch helpers, unused promise wait wrappers, and stale Redis/codegen helper entry points.
• The old async generator step driver; the code now uses build_async_step_driver_direct, and the removed variant had no call sites.
• Runtime pointer/string helpers in map/set/bigint that had been superseded by newer representation-aware paths.

Reviewed but intentionally left in place

• maybe_force_lazy, because it documents and implements lazy JSON array materialization plumbing that may be exercised by future accessor paths.
• write_stream_end1_impl, because it appears to be intended support for writeStream.end(chunk) even though the current method table only registers the zero-argument form.
• create_fs_constants_object, because it is a compatibility-style runtime helper for fs.constants; removing it would be riskier than the warning suggests.
• JSON/SSO helpers such as sso_emit_enabled, nanbox_pointer_f64, and stringify_value_with_replacer, because they are tied to partially wired migration or replacer support.
• WebSocket pump declarations and JS runtime conversion helpers, because they are feature/API-facing surfaces rather than obviously disposable code.
• CLI helpers such as compile_for_web, merge_p12_files, get_type_at_position, and encode_nil, because they look like unfinished or externally useful capabilities rather than safe dead-code removals.

Validation

• git diff --check
• cargo build

The build still reports unrelated warnings for unreachable patterns, unused fields, feature-gated declarations, and intentionally retained helper functions. This PR focuses only on functions that were clear to remove or narrow safely.