feat: add Homebrew cask support

[dbydd]

Summary

• add an in-repo Homebrew cask for Mouser on macOS
• document brew installation in the main README and macOS guide
• add a GitHub Actions workflow plus helper script to keep the cask version aligned with releases

Validation

• brew style Casks/mouser.rb
• python3 -m py_compile scripts/update_homebrew_cask.py
• python3 scripts/update_homebrew_cask.py --check --event-path /tmp/mouser-release.json
• python3 scripts/update_homebrew_cask.py --check --event-path /tmp/mouser-tag-only.json

Closes #29

[farfromrefug]

@dbydd the cask update process seems really complicated. As you only need to update the release we should simply add a step in the release workflow to regexp replace the version with the one we are publishing.
Plus it would be better to have that all handled in one workflow: the release workflow