CI: refactor iperf3 UDP analysis function

- Add helper function to normalize bitrate values to Mbps for calculations.
- Add helper function to extract data from iperf test report.
- Clean up the UDP analysis function, improve test report formatting.
- Fix an issue where Gbps values were incorrectly reported due to inconsistent
  unit parsing.
- Update CI unit test report checks to match the new formatting.

ci-scripts/tests/log/iperf_udp_msg_nok.txt

@@ -1,4 +1,4 @@
-Sender Bitrate  : 0.52  Mbps
-Receiver Bitrate: 0.52  Mbps (too low! < 99%)
+Sender Bitrate  : 524.00 Kbps
+Receiver Bitrate: 524.00 Kbps (52.40%) (too low! < 99%)
 Jitter          : 0.026 ms
-Packet Loss     : 10 % (too high! > 0%)
+Packet Loss     : 10% (too high! > 0%)