Add extract_url_credentials() function to parse HTTPS URLs with embedded
credentials (https://user:pass@host/path). Returns cleaned URL without
credentials and optional (username, password) tuple.
- Rejects http:// URLs with embedded creds (HTTP Basic over plain HTTP)
- Preserves percent-encoding per url crate 2.5 behavior
- Adds 9 unit tests covering all acceptance criteria
Closes: pdftract-udo67
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
