Add better dtype preservation in astronomy functions with numpy 2

[djhoese]

Using numpy 2 is revealing a lot of spots in the astronomy functions where 32-bit floats/datetimes are being promoted/upcasted to 64-bit floats. This PR is an overhaul of type annotations and tests and dtype checks in order to try to clean this up a bit. But with all the type annotations it has started to get less clean. I've always had trouble though with understanding what arguments were what type so hopefully this is a start toward better descriptions of those.

• Closes #xxxx
• Tests added
• Tests passed
• Passes flake8 pyorbital
• Fully documented

[codecov]

Codecov Report

Attention: Patch coverage is 92.47312% with 7 lines in your changes missing coverage. Please review.

Project coverage is 88.02%. Comparing base (18340ca) to head (23ada80).
Report is 32 commits behind head on main.

Files with missing lines	Patch %	Lines
pyorbital/astronomy.py	92.30%	4 Missing ⚠️
pyorbital/tests/test_astronomy.py	92.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #155      +/-   ##
==========================================
+ Coverage   87.51%   88.02%   +0.51%     
==========================================
  Files          14       14              
  Lines        2210     2247      +37     
==========================================
+ Hits         1934     1978      +44     
+ Misses        276      269       -7     

Flag	Coverage Δ
unittests	88.02% <92.47%> (+0.51%)	⬆️

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[coveralls]

coverage: 87.965% (+0.4%) from 87.562%
when pulling 23ada80 on djhoese:bugfix-dtype-promotion
into 83e029a on pytroll:main.

[mraspaud]

closing this one, as it is not relevant right now anymore. Feel free to reopen in the situation changes.