v0.6.0

midi2cpp now bundles the midi2 C99 core (vendored amalgam in src/), so a
consumer imports one library. The external midi2 dependency is removed from
library.properties, library.json, idf_component.yml, and CMakeLists.txt.
Bundles midi2 0.6.0. A standalone midi2 install coexists.

Fixed

• Host no longer drops inbound messages under a burst. Host::feedRx ran the
  full UMP decode + dispatch synchronously, so calling it from a platform RX
  callback starved the USB service and the non-overwritable RX FIFO truncated
  under high message rates. The host recipes hit this on machine-gun inputs.

Added

• midi2_rx_ring.h: an SPSC ring (the "stream core") that decouples the USB
  receive path from message processing, mirroring the queue/drain split proven
  on the ESP32 host transport. Header-only, drop-newest, lock-free for one
  producer and one consumer.
• Host::rxDropped() reports packets refused on a full RX ring (0 = clean);
  size the ring with MIDI2CPP_HOST_RX_RING (default 256).

Changed

• Host::feedRx now only enqueues the inbound UMP (O(1), no decode) into the
  RX ring, so it is safe to call straight from a TinyUSB rx_cb. The decode +
  dispatch moved into Host::task(), which drains the ring on the main loop.
  Callbacks fire from task(), not from feedRx; recipes that already call
  task() each loop iteration need no change. Bridge inherits the fix through
  Host::feedRx / Host::task().