Drop MPU-9250 driver and remove embd dependency

The MPU-9250 is an older chip and the Raspberry Pi kernel ships no
inv_mpu6050 driver, so migrating it to the kernel IIO path the way
BMP280 and ICM-20948 went would mean shipping yet another out-of-tree
module. Not worth the upkeep — drop the driver instead. With it gone,
kidoman/embd has no remaining consumers, so the require and the
westphae/embd replace (the +rpt kernel-version workaround) come out too.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

AHRS 0.6.0

First semver-tagged release of the modernized goflying:
- Go modules layout
- AK09916 magnetometer support on icm20948 (bypass mode, AK09916 axes)
- Block-read accel/gyro/temp, transient I/O recovery, TEMP_CONFIG DLPF
- TUI test program for icm20948
- westphae/embd-fork replace for modern Raspberry Pi OS kernel strings

Make them useful.

Sleep a little more before turning on MPU9250 reads.

Sleep a little more before turning on MPU9250 reads.

Sleep a little more before turning on MPU9250 reads.

MPU9250 driver incorrectly assumed gravity on z axis.

Smooth the AHRS values a bit more.

mpu9250 driver calibration not as sensitive.

mpu9250 driver calibration not as sensitive.