v0.4.1

• New node: ChannelCrossfade
• RectangularEnvelope: Rename from EnvelopeRect for consistency with other Envelope classes
• Node: Add is_playing property
• Node: Refactor play/stop error handling to use NodeAlreadyPlayingException, NodeNotPlayingException, CPUUsageAboveLimitException
• BufferPlayer: Add position property
• Buffer: Add filename read-only property
• SawLFO, SawOscillator: Implement phase reset with trigger
• Granulator: Add support for negative playback rates, stereo input
• signalflow_midi: Add support for MIDIManager per-channel binding
• Add wheel for Python 3.12