codal_app: Update codal-microbit-v2 to v0.2.54.

Changes to codal-core:
- updated streams API to include connection checks by API requirement
- fixed the level detectors to correctly handle initial connections to
  their upstream
- removed duplicate documentation in cpp
- adjusted CODAL_STREAM_IDLE_TIMEOUT_MS down to 75ms
- added async and sync variants of play and record, for convenience
- removed unusued bool and check for timeouts in getValue

Changes to codal-microbit-v2:
- added volume and sample rate control for MixerChannels
- implemented new API requirements for Mixer2, Synth and virtual output
  pins
- improve sound quality of virtual sound pin:
    - fix bug in audio mixer that could cause one inaccurate sample at the
      start of each DMA buffer
    - enable external crystal at boot to improve frequency accuracy of
      audio playback
    - add optional CONFIG block to discretize the output of virtual sound
      pin to nearest integer divisor of mixer
    - minor codepath optimization to prevent unecessary processing in audio
      mixer
- removed old level detector

Charges to codal-nrf52:
- updated the ADC channels to use the new requirements for stream API
  classes

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": "v0.2.51",
+        "branch": "v0.2.54",
         "type": "git",
         "test_ignore": true
     } ,