esp32-a2dp-xq 0.1.0

First public release. Not yet tested with real headphones: the host tests pass and the examples
build with ESP-IDF 5.3, 5.5, 6.0, 6.1 and the Arduino core 3.1.3 and newer.

Added

• A2DP source with the Bluedroid SBC encoder, fed from a PCM FIFO (16-bit, or 32-bit with TPDF
  dither) with 300 ms of buffering in PSRAM when available.
• SBC-XQ negotiation (Dual Channel, bitpool 38, 452 kbps) with ESP-IDF 6.0 and newer, fallback to
  Joint Stereo bitpool 53 (328 kbps).
• Per-device memory of XQ results in a text file, built-in blacklist, per-device XQ switch.
• AVRCP: headphone buttons, absolute volume in both directions, own attenuation for headphones
  without absolute volume.
• Discovery with name resolution, Secure Simple Pairing and legacy PIN pairing, automatic
  reconnect, link-loss notification.
• Builds with ESP-IDF 5.3 and newer and the Arduino core 3.x; without SBC-XQ before ESP-IDF 6.0.
• Examples for ESP-IDF and Arduino.