#364 Only trim spaces and tabs around header parameters

parse_options_header trimmed parameter names and values with strip(), rstrip() and lstrip() without arguments. Those remove all Unicode whitespace, and because the header is decoded as latin-1, the bytes 0xA0 and 0x85 count as whitespace too. Whitespace around a header parameter is only a space or a tab (RFC 9110 §5.6.3).

Header	Before	After
form-data; name=voil\xc3\xa0	name is voil\xc3	name is voil\xc3\xa0
form-data; name="a";\xa0filename="a.txt"	Has filename	\xa0filename isn't filename, so the part is a field
multipart/form-data; boundary=XX\xa0	Boundary is XX	Boundary is XX\xa0

Spaces and tabs are still trimmed, and quoted values are unchanged.

AI Disclaimer

This PR was developed with the assistance of either Claude or Codex. I've reviewed and verified the changes.