Replace FMOD with SDL3_mixer

[StevenSYS]

Currently I'm using dummy FMOD header files that I made.

EDIT 2026-01-07: I've now got it to a point where it can play sounds!

[StevenSYS]

I want to add using FLAC files, MP3 files, OGG files, WAV files, etc for music instead of MIDI files