feature: Advanced Transitions with MIDI files (v0.3.0 milestone)

[piotrmacha]

Development in progress.

Goal

Implement a transition between themes based on a specifically crafted MIDI file. The MIDI file matches the theme's audio duration and tempo, and defines special note ranges (MIDI_EVENT_NOTE, press + release) for periods when a transition should be scheduled. Current scope limits the metadata to a simple cross-fade transition, with 2 possible metadata notes:

• A4 (69): Marks a period when transition can happen and the duration of volume fade-out for current theme. By default, the next theme is fading-in during the same period.
• A#4 (70): Optional, marks a different fade-in period for the next song. Must be defined with start time <= A4 end time.

Done

• MidiFile class with a parser of node ranges
• MidiFile parser supports tempo changes within single audio theme
• Refactor to move the music scheduling code directly to the MusicTheme, which responds to 3 possible events from the outside world (PlayInstant — when no other music is playing; ScheduleAfter — when other music is playing, StopInstant — usually called by the next scheduled song to stop the current), and then submits commands or acquires a channel to execute methods on it. The Channel object became just a command processor exposing an API for the MusicTheme to control playback and effects.
• Add new Daedalus classes to define zBassMusic-specific themes with additional fields like the MIDI file.
• Implement a transitions based on data from MIDI
• Add Daedalus externals to set up transitions programmatically
• Update docs to include how to create a theme using new Daedalus classes
• Update docs and include the specification for expected MIDI files and a guide on how to create them