Replace CGI.parse with internal parser for Ruby 4.0 compatibility

[Filipe Goncalves (basex)]

Problem

Ruby 4.0 slimmed down the cgi standard library and removed CGI.parse. As a result, RefererParser::Parser#parse raises when a referer URL has a query string:

undefined method 'parse' for class CGI (NoMethodError)
    query_params = CGI.parse(url.query)

(CGI.escape/CGI.unescape remain available; only CGI.parse and the larger CGI surface were removed.)

Fix

Replace the CGI.parse call with a small internal parse_query helper that returns the same Hash-of-arrays shape, using the still-available CGI.unescape for value decoding. No new dependencies, and it remains compatible with older Rubies.

Verification

Tested on Ruby 4.0.5 against real referer URLs:

• + and %XX decoding (q=hello+world, q=ruby%204)
• repeated keys (q=&q=second -> picks first non-blank)
• params present but search term absent -> nil
• no query string -> nil
• malformed/bare/empty keys (q=x&flag&=&weird) -> no longer raises

All produce the expected results; behavior matches the previous CGI.parse-based output.

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[Copilot]

Pull request overview

Note

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Updates referer query parsing to avoid relying on CGI.parse by introducing a local query-string parser.

Changes:

• Replaced CGI.parse(url.query) with a new parse_query(url.query) helper.
• Added parse_query to parse application/x-www-form-urlencoded query strings into a hash-of-arrays.

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[Filipe Goncalves (basex)]

Thanks for your pull request. Is this your first contribution to a Snowplow open source project? Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

I signed it!