Add '--list-checks' flag that lists all implemented checks

[vickgoodman]

Usage example:

$ beman-tidy --list-checks
[Requirement]    cmake.library_alias
[Recommendation] cmake.library_name
[Recommendation] cmake.project_name
[Recommendation] cpp.extension_identifiers
[Recommendation] cpp.namespace
[Requirement]    directory.docs
[Requirement]    directory.examples
[Requirement]    directory.papers
[Requirement]    directory.sources
[Requirement]    directory.tests
[Recommendation] file.copyright
[Requirement]    file.license_id
[Recommendation] file.names
[Requirement]    file.test_names
[Recommendation] library.name
[Recommendation] license.apache_llvm
[Requirement]    license.approved
[Requirement]    license.criteria
[Requirement]    readme.badges
[Recommendation] readme.implements
[Requirement]    readme.library_status
[Requirement]    readme.license
[Recommendation] readme.purpose
[Recommendation] readme.title
[Requirement]    release.github
[Recommendation] release.godbolt_trunk_version
[Recommendation] release.notes
[Requirement]    repository.code_review_rules
[Requirement]    repository.codeowners
[Requirement]    repository.default_branch
[Recommendation] repository.disallow_git_submodules
[Requirement]    repository.name
[Requirement]    toplevel.cmake
[Requirement]    toplevel.license
[Requirement]    toplevel.readme

$ beman-tidy --list-checks /path/to/repo outputs the same

[Copilot]

Pull request overview

This PR adds a new --list-checks CLI flag intended to print all implemented Beman Standard checks (with their Requirement/Recommendation type), and updates the README’s captured --help output accordingly.

Changes:

• Add --list-checks handling to the CLI, printing registered check names and their types.
• Update README --help snippet to include --list-checks (and reflect current CLI options).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
beman_tidy/cli.py	Adds --list-checks via a custom argparse action and implements check listing output.
README.md	Updates the documented --help output to include the new flag.

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[vickgoodman]

I tested this locally and beman-tidy --list-checks works without repo_path. The custom ListChecksAction exits during argument parsing before argparse performs the final required positional argument validation. Normal commands such as beman-tidy --verbose still fail with the expected missing repo_path error.

[vickgoodman]

Not relevant. See prev comment.

[vickgoodman]

Done.