Fix to xr dataset merge error with conflicting values in coordinate

[BENR0]

Fixes the merge error Problem by allowing to pass the compat argument.

• Closes MergeError in to_xarray_dataset for Scenes containing data from seviri_l1b_nc reader #2179
• Tests added
• Fully documented

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.91%. Comparing base (3c7938c) to head (aff7b96).
Report is 25 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2827      +/-   ##
==========================================
- Coverage   95.94%   95.91%   -0.03%     
==========================================
  Files         366      366              
  Lines       53504    53519      +15     
==========================================
+ Hits        51332    51335       +3     
- Misses       2172     2184      +12     

Flag	Coverage Δ
behaviourtests	4.04% <4.34%> (-0.01%)	⬇️
unittests	96.01% <100.00%> (-0.03%)	⬇️

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[djhoese]

This looks good to me except the type annotation on compat which I've commented on inline. If that is resolved then this is good to merge.

[djhoese]

The Optional type suggests this can be None, but that's not true is it?