Port more backend tests from wradlib

[kmuehlbauer]

• xradar version: 0.0.10
• Python version: 3.11
• Operating System: Linux

Description

When porting the code for the backends from wradlib to xradar I've only implemented light testing of overall functionality. I'm currently in the process to actually use xradar from wradlib, removing duplicated code.

There are a bunch of tests still at wradlib, which are better living here.

• [x] Furuno #73
• [ ] Furuno - create functions for decoding raw data
• [x] Iris/Sigmet #73
• [x] Rainbow #73
• [x] Odim - might need rewrite from scratch #154
• [x] Gamic - might need rewrite from scratch #154

[kmuehlbauer]

While exploring #138, #139 I've found that a lot of functionality in some backends is not test-friendly abstracted into functions/methods. Instead it needs a file to test the workflow.

Let's use this issue to keep track of wanted/needed changes.