Fix core: harden config and fullwidth paths

[PeterDaveHello]

Improve error context on config lock failures.
Handle empty filenames safely in get_file_extension. Inline fullwidth mapping to keep behavior explicit and predictable. No behavior change expected in normal cases; adds clearer diagnostics and edge-case guards.

GitHub Copilot summary:

This pull request focuses on improving code safety, clarity, and maintainability by refining error handling, removing unnecessary data structures, and making code more robust against edge cases. The most significant changes are grouped below:

Error Handling Improvements

• Replaced all unwrap() calls on lock acquisition for CURRENT_CONFIG with expect() calls that provide explicit error messages, making failures easier to debug. (autocorrect/src/config/mod.rs) [1] [2]

Code Robustness

• Updated the get_file_extension function to use unwrap_or instead of unwrap when splitting filenames and extracting extensions, which prevents panics on unexpected input. (autocorrect/src/code/types.rs)

Code Simplification and Performance

• Removed the FULLWIDTH_MAPS HashMap and replaced it with a direct match statement in fullwidth_replace_part, reducing overhead and improving code clarity. (autocorrect/src/rule/fullwidth.rs) [1] [2]

Minor Refactoring

• Changed the merge method in Config to iterate over references and clone keys/values as needed, improving efficiency and code readability. (autocorrect/src/config/mod.rs)