feat(source): implement source@v1 role and input stream protocol

[rudyberends]

This PR adds a working source@v1 reference implementation to aiosendspin.

It covers the full flow:

• source handshake support (source@v1_support)
• source state + source commands
• source binary audio chunks (message type 12)
• input stream messages:
  • input_stream/start
  • input_stream/request-format
  • input_stream/end
• server-side source role handling and ingest into normal group playback
• controller state integration with optional sources list

changes

• Added source models in aiosendspin/models/source.py
• Extended core/types/client for source + input stream messages
• Added server roles:
  • server/roles/source/v1.py
  • server/roles/source/group.py
• Wired source role into role registry and connection dispatch
• Added source tests:
  • tests/models/test_source_models.py
  • tests/server/roles/test_source_v1.py