Add production-grade lint configuration (clippy, rustfmt)

- Configure strict clippy lints in Cargo.toml: forbid unsafe, deny
  correctness issues, warn on perf/suspicious/style patterns
- Add rustfmt.toml (max_width=100) and clippy.toml (thresholds)
- Fix all lint violations: replace `as` casts with proper try_from
  conversions, add TooManyGlyphs error variant, use font-types
  BigEndian path for method references, inline format args
- Update CI to run clippy with --all-targets