style: Migrate to stable-only rustfmt configuration

- Remove nightly-only features from .rustfmt.toml and vendor/ss58-registry/rustfmt.toml
- Removed features: imports_granularity, wrap_comments, comment_width,
  reorder_impl_items, spaces_around_ranges, binop_separator,
  match_arm_blocks, trailing_semicolon, trailing_comma
- Format all 898 affected files with stable rustfmt
- Ensures long-term reliability without nightly toolchain dependency

pezkuwi/tests/benchmark_block.rs

@@ -15,7 +15,6 @@
 // along with Pezkuwi.  If not, see <http://www.gnu.org/licenses/>.
 
 #![allow(deprecated)]
-
 // Unix only since it uses signals.
 #![cfg(unix)]