feat(googlefonts): add no_oblique_bit check

[felipesanches]

Summary

• Adds new check googlefonts/no_oblique_bit that FAILs when OS/2 fsSelection OBLIQUE bit is set
• Google Fonts explicitly does not want this bit enabled (Red Hat fonts had both Italic and Oblique set)
• Google Fonts profile, includes Rust test

Closes #238

Test plan

• cargo test --workspace passes (0 failures)
• cargo clippy --all -- -D warnings clean
• cargo fmt --all -- --check clean

Note: This PR was generated by an AI agent (Claude) working under the guidance of @felipesanches, but submitted without human review. @felipesanches himself would still need to participate in the PR thread if he wants to contribute to the review.

🤖 Generated with Claude Code

[simoncozens]

Please add a hotfix function which turns off this bit.

[felipesanches]

Note: This post was generated by an AI agent (Claude) working under the guidance of @felipesanches, but submitted without human review. @felipesanches himself would still need to participate in the PR thread if he wants to contribute to the review.

Done! Added a hotfix function fix_no_oblique_bit that clears the OBLIQUE bit (bit 9) from OS/2.fsSelection. It follows the same pattern as the use_typo_metrics hotfix — reads the OS/2 table, removes the SelectionFlags::OBLIQUE flag, and rebuilds the font.

Also added a test (test_hotfix_clears_oblique_bit) that creates a font with the OBLIQUE bit set, applies the hotfix, and verifies the check passes afterward.