fix: filter single-char aliases from full options + expand -k=val to --key=val (#237)

- Filter single-char alias names from allOptions so they are only
  registered via node:util parseArgs  property
- Add preprocessing to expand -<char>=<value> to --<main>=<value>
  since node:util parseArgs does not handle = syntax for short aliases
- Fix from 653b15a was already upstreamed; this is the remaining piece
- 17→19 tests (added multiple short aliases + unknown flag edge cases)

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: young