Extend self-tests

[mndza]

This PR enhances the transceiver loopback self-tests by adding more validation checks and including tests for the narrowband filter.

[mndza]

Updated the self-test report to always include raw measurements from the loopback test. The output now appears as:

Self-test result: PASS
Mixer: RFFC5072, ID: 4416, Rev: 1
Clock: Si5351, Rev: 1, readback: OK
Transceiver: MAX2831, RSSI mux test: PASS
FPGA configuration: PASS
SGPIO RX test: PASS
Loopback test: PASS
 0:1039,1027,64,60,1305,1348
 1:1024,1025,62,59,1315,1380
 2:4079,4081,54,51,885,936
 3:972,1129,37,11,4,1

I also considered encoding the measurements in hexadecimal to save space. Thoughts?

[mndza]

Added new results for the selftests: skipped and timeout.