Importers for new OPERA products

[pulkkins]

Production of ODYSSEY radar composites from OPERA was discontinued on October 30th 2024. They have been replaced with CIRRUS and NIMBUS. This pull request contains

• ODIM HDF5 importer with support for the new OPERA products (backward compatible with ODYSSEY)
• updated test module for ODYSSEY, CIRRUS and NIMBUS

Example data from CIRRUS and NIMBUS has been uploaded here.

As stated here, the ODIM HDF5 importer should be able to read HDF5 files from DPC. Could someone add tests for those?

[codecov]

Codecov Report

Attention: Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.

Project coverage is 84.17%. Comparing base (8b5333c) to head (11c04fe).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pysteps/io/importers.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #441      +/-   ##
==========================================
+ Coverage   84.03%   84.17%   +0.14%     
==========================================
  Files         160      160              
  Lines       13031    13058      +27     
==========================================
+ Hits        10950    10991      +41     
+ Misses       2081     2067      -14     

Flag	Coverage Δ
unit_tests	84.17% <94.59%> (+0.14%)	⬆️

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[dnerini]

looking all good, thanks a lot @pulkkins for this contribution!

concerning the compatibility with DCP files, I suggest to open a separate issue.