Reject a trailing newline in email local parts

[fhgffy]

The local-part pattern accepts a final newline before the at-sign because re.match() and $ can leave that character unconsumed. For example, email("person\n@example.com") currently returns True.

Use re.fullmatch() to require the local part to consume the entire value. The regression covers an ordinary name, a dotted name, an extended-Latin name, and a quoted name, with valid controls for each. All four newline cases fail on the unchanged source.

On Python 3.12.2, pytest . -q passes with 1131 tests. Ruff lint and format checks, Pyright, Bandit, and wheel/sdist builds also pass.

The open terminal-newline fix in #501 covers MAC and regional identifier validators; this change covers email local parts.