fix: use synthesize_mono_midi directly with explicit instrument_id

debug: print synthesize_midi signature and output before subscripting

fix: inspect synthesize_midi signature at runtime to adapt to installed version

fix: remove use_fluidsynth_for_invalid_midi (not in this version)

fix: run midi_ddsp_download_model_weights before load_pretrained_model

initial MIDI-DDSP HARP deployment