Add tests for binary file detection when using memory maps

[Erio-Harrison]

The original code contained a TODO comment to add tests for binary file detection
when using memory maps. This PR implements those tests, noting the differences
between mmap and no-mmap behavior regarding binary detection.

The tests show that with memory maps:

• NUL bytes are only searched for in the first few KB and in matches
• Explicit file paths behave differently than glob patterns
• Matches can appear both before and after NUL bytes
• Binary detection is more permissive with memory maps