gh-153823: Parse apostrophes in unquoted MIME parameter values

[lpyu001]

Summary

Fixes gh-153823.

email.policy.default incorrectly treated apostrophes as delimiters in all unquoted MIME parameter values. Apostrophes are not MIME tspecials, so values such as filename=O'Brien.pdf and multipart boundaries containing apostrophes are valid tokens.

This change:

• parses regular unquoted parameter values using MIME token syntax;
• preserves existing RFC 2231 extended-value handling and error recovery;
• adds regression tests for filenames, multipart boundaries, and header registry parsing.

• Issue: email: unquoted apostrophe in a MIME parameter value is dropped under policy.default #153823