fix: load libopenmpt on demand

What does this PR do? (Please give us a brief description of what this PR does.)

only load libopenmpt on demand (when loading the file to play). this reduces the initial page load size by up to 500kb gzipped. ideally MkModPlayer itself should be loaded lazily, but that's for another time i guess

should also fix any race conditions that occurred when the wasm module wasn't loaded yet but the player tried to start playing, as well as the player itself not working at all when running locally with vite devserver

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