perf(goto): reuse cookie jar while parsing headers

[Kikobeats]

Note

Low Risk
Low risk: small, localized change to cookie parsing that mainly affects performance and cookie-header edge cases; behavior changes are covered by a new unit test.

Overview
parseCookies now reuses a single tough-cookie CookieJar per cookie header and parses cookies via the returned cookie object (toJSON()), skipping entries that fail to set.

Adds a unit test that monkeypatches tough-cookie to assert only one CookieJar is constructed during parsing.

^{Written by Cursor Bugbot for commit 3e7bedf. This will update automatically on new commits. Configure here.}