Add reader for GMS-5 VISSR data

Add reader for GMS-5 VISSR data. This is still a work in progress:

• No calibration yet, only counts.
• Geolocation is pretty slow
• Not compatible with dask, yet

• [ ] Closes #xxxx
• [ ] Tests added
• [ ] Fully documented
• [ ] Add your name to AUTHORS.md if not there already

What is the status of this? Could this be merged, since it still can be useful to some, and then open new PRs to add calibration, daskification, etc?

@mraspaud I'm gonna continue here this autumn probably. But it's a good idea to merge this version and add more features later. I'll try to get this into a merge-able state in the upcoming weeks.

Codecov Report

Merging #2117 (3a92014) into main (4f6a7c3) will increase coverage by 0.13%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2117      +/-   ##
==========================================
+ Coverage   94.83%   94.96%   +0.13%     
==========================================
  Files         337      343       +6     
  Lines       49430    50710    +1280     
==========================================
+ Hits        46875    48155    +1280     
  Misses       2555     2555              

Flag	Coverage Δ
behaviourtests	4.32% <0.00%> (-0.11%)	:arrow_down:
unittests	95.56% <100.00%> (+0.11%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/readers/gms/gms5_vissr_format.py	100.00% <100.00%> (ø)
satpy/readers/gms/gms5_vissr_l1b.py	100.00% <100.00%> (ø)
satpy/readers/gms/gms5_vissr_navigation.py	100.00% <100.00%> (ø)
...tpy/tests/reader_tests/gms/test_gms5_vissr_data.py	100.00% <100.00%> (ø)
...atpy/tests/reader_tests/gms/test_gms5_vissr_l1b.py	100.00% <100.00%> (ø)
...sts/reader_tests/gms/test_gms5_vissr_navigation.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/utils.py	100.00% <100.00%> (ø)

... and 22 files with indirect coverage changes

Pull Request Test Coverage Report for Build 5348733749

• 1067 of 1067 (100.0%) changed or added relevant lines in 7 files are covered.
• 217 unchanged lines in 12 files lost coverage.
• Overall coverage increased (+0.1%) to 95.518%

---

Files with Coverage Reduction	New Missed Lines	%
satpy/writers/ninjogeotiff.py	1	99.3%
satpy/readers/fci_l1c_nc.py	5	98.02%
satpy/composites/init.py	6	91.24%
satpy/readers/avhrr_l1b_gaclac.py	6	95.68%
satpy/tests/writer_tests/test_ninjogeotiff.py	8	96.67%
satpy/readers/olci_nc.py	11	94.2%
satpy/readers/hrit_base.py	17	86.61%
satpy/readers/geocat.py	18	88.82%
satpy/readers/seviri_l1b_hrit.py	25	91.25%
satpy/readers/seviri_l1b_nc.py	37	74.36%
<!--	Total:	217

Totals
Change from base Build 5005892017:	0.1%
Covered Lines:	48268
Relevant Lines:	50533

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💛 - Coveralls

@sfinkens this looks good! I'm just wondering if the 3 gms5 files should be in their own subpackage under readers?

Good idea, done!

Just had a quick look through the code, all looks good to me!

Just had a quick look through the code, all looks good to me!

Thanks for taking the time!