Add mixed EK80 WBT/GPT CW file as integration test

[LOCEANlloydizard]

We identified a good regression/integration test file: 1907RL_CW-D20190810-T215906.raw

A mixed EK80 CW file with:

• 4 WBT channels in Sonar/Beam_group1 → complex
  • ES333 / ES200 / ES70 / ES120
• 1 GPT channel in Sonar/Beam_group2 → power
  • ES38B

This file exposed mixed-configuration edge cases during calibration debugging, so it would be a useful integration/regression test candidate.

TODO:

• Add file to GitHub assets (zarr format)
• Add CI integration coverage using this file
• Add file metadata/config note in the relevant test-data README (see Add missing test data README to release assets and inventory all test files #1565)