[refactor] Reality OS: cleaning dead code from Typer's vendored Click

[wallerphilip-cpu]

I'm working on a cleanup of Typer as part of "Reality OS" — removing unused code from the vendored Click compatibility layer.

Initial scan with vulture (80% confidence) found ~10 unused imports/variables:

• typer/_click_compat.py:415 (delete)
• typer/_click_winconsole.py:79,81 (Buffer)
• typer/_click/parser.py:37-38 (CoreArgument, CoreOption)
• typer/cli.py:167 (version)
• typer/completion.py:65,72,84,90 (install_completion, show_completion)

Plus the already-removed unused TYPE_CHECKING import in testing.py (PR #1845).

Plan:

1. Remove confirmed dead code
2. Ensure 100% test coverage stays green
3. No API changes

Opening this discussion before the PR as requested in CONTRIBUTING. Happy to break it into smaller PRs if preferred.

[svlandeg]

Thanks for the note and the offer 🙏

There's no need to PR this though, as we're actively working on refactoring the vendored Click code, and the PR you'd submit would only conflict with ongoing work. We also prefer to do this with substantial human oversight, as this will set the foundation for future Typer. The core maintainers team will be in charge of leading this effort 😉