codal_app: Update codal-microbit-v2 to v0.2.51.

Changes to codal-core:
- streamSplitters now emit finer-grained events
- introduce Pin Disconnecting flag
- only wipe specified region on large ManagedBuffer::shift
- reworked and updated the streams API
- add rms based clap detection to level detector spl
- set default DEVICE_DMESG_BUFFER_SIZE based on DMESG_ENABLE
- updated DataStream to support decoupling the input fiber from the output
  to enable async stream data
- updated StreamRecording to use the new PR/Pull metrics

Changes to codal-microbit-v2:
- MicroBitRadio: fix setFrequencyBand() and do not reset tx power and
  frequency band in enable()
- simplify the BLE - Device Info - Model Number to only indicate V2
- added a small patch to confirm that all splitter channels have gone
  before turning the microphone off
- introduce sound playback "until playback complete" option
- fixed the stream wiring in MicroBitAudio
- add UX feature: Triple-tap-reset to enter pairing mode
- remove target.json DEVICE_DMESG_BUFFER_SIZE to use default
- updated MicroBitAudio and the Mixer to correctly work with the new
  streams API

Charges to codal-nrf52:
- prevent recursive disconnet loops in NRF52Pin and accidental erasure of
  obj state

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

src/codal_app/codal.json

@@ -2,7 +2,7 @@
     "target": {
         "name": "codal-microbit-v2",
         "url": "https://github.com/lancaster-university/codal-microbit-v2",
-        "branch": "v0.2.48",
+        "branch": "v0.2.51",
         "type": "git",
         "test_ignore": true
     } ,