HTTP mock: parse query and form parameters the way Symfony encodes them #106

Part of #100. Line numbers refer to branch chore/php-8.4-dependabot (#98). Verified = reproduced, suspected = from reading the code.

Several query and form values are parsed differently from what Symfony actually sends. Fixing this changes which mocks match, so it is planned for 8.0.

• explode('=') has no limit, so ?t=YQ== is parsed as YQ and base64 cursors never match (RealRequestFactory.php:157). Verified.
• Symfony's query option encodes arrays as ids[0]=1&ids[1]=2 and filter[a]=1. These are parsed into flat keys, so none of these ever match: queryParam('ids[]', …), queryParam('ids', [...]), queryParam('filter', [...]) (RealRequestFactory.php:147-178). Verified.
• queryParam('ids[]', ['1', '2']) doesn't match even ?ids[]=1&ids[]=2 (Matcher/QueryParamMatcher.php:58). Verified.
• Form bodies have the same problems: t=YQ== is truncated, and array fields become tags[0], so requestParam('tags[]', …) never matches (RealRequestFactory.php:83-88). Verified.

Breaking: mocks written against the current parsing, e.g. queryParam('t', 'YQ'), stop matching.