Add runtime regex checks

[Lukas616]

No description provided.

[Lukas616]

Summary

Adds runtime-configurable regex checks through --checks / --check-config.

• Supports JSON config files with a checks array
• Each check defines field, regex, alert, and optional ignore_case
• Supports domain fields, record fields, HTTP status/content-length fields, and response body content
• Emits [REGEX] alerts with the custom alert text when a configured pattern matches
• Truncates long matched values in alerts so response-body matches stay readable
• Keeps response body text in memory for matching only; it is not written to JSON output
• Documents the config format and supported fields in the README
• Includes small build compatibility updates needed by current macOS/Homebrew builds

Checks

• Configured with CMake
• Built successfully
• Confirmed --checks appears in --help
• Ran a config-driven smoke check against example.com for domain, type, and response_body
• Confirmed unsupported fields are rejected with a clear error
• Confirmed response body text is not written to the JSON output

Payment can be sent here: https://paypal.me/Lukas61616