samples: sensor_shell: add fake sensor driver & pytest

[ycsin]

Add a fake sensor driver so that the sample can be played with in a more meaningful way.

Then, use pytest to test the shell commands.

Sample doc preview

[ycsin]

Updated the fake driver to handle 3-axis data properly:

uart:~$ sensor get sensor@0 4
channel idx=7 gyro_xyz shift=0 num_samples=0 value=4294967295ns, (-0.000000, -0.000000, -0.000000)
[870:26:48.134,000] <inf> fake_sensor: [sample_fetch] dev: 0x8000e2b8, chan: 59
[870:26:48.134,000] <inf> fake_sensor: [channel_get] dev: 0x8000e2b8, chan: 4
uart:~$ sensor get sensor@0 7
channel idx=7 gyro_xyz shift=3 num_samples=1 value=9220133425350000000ns, (7.000000, 7.000000, 7.000000)
[870:26:48.134,000] <inf> fake_sensor: [sample_fetch] dev: 0x8000e2b8, chan: 59
[870:26:48.134,000] <inf> fake_sensor: [channel_get] dev: 0x8000e2b8, chan: 7
uart:~$ sensor get sensor@0 11
channel idx=11 magn_xyz shift=4 num_samples=1 value=9220133425350000000ns, (11.000000, 11.000000, 11.000000)
[870:26:48.134,000] <inf> fake_sensor: [sample_fetch] dev: 0x8000e2b8, chan: 59
[870:26:48.134,000] <inf> fake_sensor: [channel_get] dev: 0x8000e2b8, chan: 11
uart:~$ sensor get sensor@0 12
channel idx=12 die_temp shift=4 num_samples=1 value=9220133425350000000ns (12.000000)
[870:26:48.134,000] <inf> fake_sensor: [sample_fetch] dev: 0x8000e2b8, chan: 59
[870:26:48.134,000] <inf> fake_sensor: [channel_get] dev: 0x8000e2b8, chan: 12

@teburd @ubieda @jeppenodgaard PTAL again, thanks

[ycsin]

Update the test with the new sensor shell output and now the CI pass

@teburd @ubieda @jeppenodgaard @MaureenHelm PTAL again, thanks