Expand MIME type lookup to support more extensions

[JacobBorden]

Expanded the HTTP::GetMimeType function in src/http.cpp to support more extensions (json, txt, xml, webp, svg, pdf, csv, mp3, mp4). Added comprehensive unit tests in tests/http_server_tests.cpp to verify that all supported MIME types are correctly resolved, and updated the TODO.MD file to mark this task as done.

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PR created automatically by Jules for task 18149242283076851248 started by @JacobBorden

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