Add helper-function for reading SEVIRI L1.5 Native header.

[sjoro]

This PR introduces a helper function read_header in seviri_l1b_native-module. A need for this arises from EUM Helpdesk user inquiries, occurring every now and then, for asking how to read or get the header of the file for checking that their implementations in another software is correct.

The usage of the new feature is very simple:

from satpy.readers.seviri_l1b_native import read_header
hdr = read_header('MSG4-SEVI-MSG15-0100-NA-20210302124244.185000000Z-NA.nat')
print(hdr['15_DATA_HEADER']['SatelliteStatus']['SatelliteDefinition'])

• Tests added
• Fully documented

[codecov]

Codecov Report

Merging #2480 (0ae0b78) into main (bc9c089) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2480   +/-   ##
=======================================
  Coverage   94.82%   94.83%           
=======================================
  Files         337      337           
  Lines       49406    49421   +15     
=======================================
+ Hits        46851    46866   +15     
  Misses       2555     2555           

Flag	Coverage Δ
behaviourtests	4.43% <0.00%> (-0.01%)	⬇️
unittests	95.45% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
satpy/enhancements/__init__.py	99.03% <ø> (ø)
satpy/readers/seviri_l1b_native.py	86.50% <100.00%> (+0.10%)	⬆️
satpy/tests/reader_tests/test_seviri_l1b_native.py	100.00% <100.00%> (ø)

[coveralls]

Pull Request Test Coverage Report for Build 4992633853

• 36 of 36 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.001%) to 95.399%

---

Totals
Change from base Build 4960323333:	0.001%
Covered Lines:	46979
Relevant Lines:	49245

---

💛 - Coveralls

[sjoro]

any suggestions on what's going on with the docs build? this seems to be an issue which arose when i merged the latest main to my branch.

[djhoese]

/home/docs/checkouts/readthedocs.org/user_builds/satpy/conda/2480/lib/python3.10/site-packages/satpy/enhancements/__init__.py:docstring of satpy.enhancements._jma_true_color_reproduction:6: ERROR: Unexpected indentation.
/home/docs/checkouts/readthedocs.org/user_builds/satpy/conda/2480/lib/python3.10/site-packages/satpy/enhancements/__init__.py:docstring of satpy.enhancements._jma_true_color_reproduction:7: WARNING: Block quote ends without a blank line; unexpected unindent.

I'll see if I can recommend a fix. One sec...

[djhoese]

Docs are fixed now 😉

[djhoese]

I probably should have asked you before merging this, but I got impatient because now I need these doc fixes. Hopefully this PR was ready enough.

[sjoro]

it is/was for me, unless the implementation should have been preferred done in some other way... e.g. using staticmethods in NativeMSGFileHandler and then at the end of the module do something like read_header = NativeMSGFileHandler.read_header

[sfinkens]

Nice feature, thanks!