refactor(allocator): Feature gate nightly

[kdy1]

Description:

Feature gate nightly, and make it really identical to types from std if it's not enabled.

We need to use #[fundamental] for swc_allocator::boxed::Box. Without it, it will be very hard to use the type. But it's not stabilized. So we feature gate them under a cargo feature flag.

Related issue:

• Blocks refactor(visit): Pre-generate visitor code #9262

[kdy1]

swc-bump:

• swc_allocator

[kdy1]

This was the wrong way. We may need to drop support for stable rustc

[codspeed-hq]

CodSpeed Performance Report

Merging #9265 will not alter performance

_{Comparing kdy1:allocator-rustc (9f1b217) with main (6ddbfa0)}

Summary

✅ 178 untouched benchmarks