perf: skip the imported map again for local constants in `Environment.hasUnsafe`

This PR makes `Environment.hasUnsafe` look up constants that are not imported with `findAsyncCore?`, as `findAsync?` would search the imported map again, and documents why imported constants are looked up directly.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
1 file changed