gh-128982: Revert "#128982: Substitute regular expression in http.cookiejar.join_header_words for an efficient alternative (GH-128983)" and add tests

[encukou]

Revert "#128982: Substitute regular expression in http.cookiejar.join_header_words for an efficient alternative (GH-128983)"

This reverts commit 56e1900.

Add additional tests.

• Issue: Improve performance of http.cookiejar.join_header_words #128982

[hugovk]

These tests also pass on main (with #128983 / 56e1900), can we add one that fails before this revert?

[hugovk]

Sorry! I had a branch mixup, these are indeed failing on main 👍

[encukou]

I'm glad I'm not the only confused reviewer today ^^;