chore: rustfmt permissions/lib.rs with project import-granularity config
The permissions split commit landed with `cargo fmt` defaults instead of
the project's `imports_granularity=item, group_imports=StdExternalCrate`
config from .dprint.json's exec hook, leaving 22 lines that fail the
project-specific dprint check. Reformat with the right config so the
lint job passes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>