Move to using proper HWMv2 board extensions
https://docs.zephyrproject.org/4.1.0/hardware/porting/board_porting.html#board-extensions
for extending upstream Zephyr boards for use with ZMK. With this change,
using upstream Zephyr board IDs directly, e.g. `seeeduino_xiao` will be
stock versions as found upstream. To use a board variant that is tuned
for ZMK use, use the `zmk` variant, e.g. `seeeduino_xiao//zmk` which is
shorthand for `seeeduino_xiao/samd21g18a/zmk`.
* Enhance the BLE test runner to build additional peripheral builds
when detecting peripheral*.overlay files in the test.
* Add basic and multiple-peripheral tests to exercise the testing
support
* Add test for triggering local behaviors on split peripherals.
fix(ble): Fix building split code w/o settings
* Properly exclude storing peripheral addresses to settings when
settings support isn't turned on.
* Add security related tests to verify behavior when trying to read
a GATT characteristic from our peripheral with and without client
auto security request/retry.
Peter Johanson
Tygo van den Hurk