65650 functions status header

[pbearne]

This PR introduces a new test class Tests_Functions_StatusHeader to provide PHPUnit test coverage for the status_header() function in wp-includes/functions.php.
The tests cover:
•Standard HTTP status codes (200, 404, 301) and their default descriptions.
•Custom status descriptions provided as the second argument.
•Handling of unknown status codes (early return vs. using custom description).
•Verification that the server protocol (e.g., HTTP/1.1) is correctly respected in the generated header.

Since header() calls are difficult to test directly in a CLI environment, these tests rely on the status_header filter to intercept and verify the generated header string.

Trac ticket: https://core.trac.wordpress.org/ticket/65650

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•Used for: Code analysis, test implementation, and workflow management.

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