Preserve multichar option name in parser errors

[Ajeem-git]

Summary

• preserve the longest matching multichar single-dash option when long-option matching falls through
• avoid degrading -dbgwrong into a misleading -d parser error
• add a regression test covering the reported behavior

Testing

• PYTHONPATH=src ./.venv311/bin/python -m pytest -q tests/test_options.py -k "unknown_options or multichar_short_option_reports_full_option"
• direct CliRunner repro now reports No such option: -dbg

Closes #2779