Fix CAPTCHA hostname verification when providers return parent domains

[itsvelle]

Fixes #3549

This pull request improves the CAPTCHA hostname verification logic to be more robust and accurate, especially when dealing with parent domains returned by some CAPTCHA providers. The main changes introduce a new hostname matching function, update the verification logic to use it, and add tests to ensure correct behavior.

Hostname verification improvements:

• Added a new normalize_hostname function to ensure hostnames are compared in a case-insensitive manner and without trailing dots.
• Introduced the hostname_matches_site function, which allows the CAPTCHA response hostname to match either exactly or as a parent domain of the site hostname. This accommodates providers that return only the registrable domain.
• Updated the CAPTCHA verification logic in the Form implementation to use the new hostname_matches_site function instead of a strict equality check.

Testing improvements:

• Added a new test module to verify the correctness of the hostname matching logic, including cases for exact matches, parent domains, similar suffixes, case insensitivity, and trailing dots.

[CLAassistant]

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