global ephemeris data cache

[nicHoch]

add a internal ephemeris data cache. This allows to save hidden fido search and download of the same data multiple times

All coordinate transform and imaging methods might internally search for correct ephemeris data for higher precession.
To get the ephemeris data a FIDO search (defaults to our stix data server) is uses and data gets downloaded.

The ephemeris data search utilises a global cache in order to avoid unnecessary network traffic or file loading. ANC ephemeris fits files are organised as daily files. The entire day is put to cache if touched once.

A user can prefetch or pinpoint specific ephemeris data files with the `load_ephemeris_fits_to_cache(filename)' method.

    from stixpy.coordinates.transforms import load_ephemeris_fits_to_cache

    start_time = Time("2023-01-01T12:00:00")
    end_time = Time("2023-01-01T12:30:00")
    query = Fido.search(
        a.Time(start_time, end_time),
        a.Instrument.stix,
        a.Level.anc,
        a.stix.DataType.asp,
        a.stix.DataProduct.asp_ephemeris,
    )

    aux_files = Fido.fetch(query["stix"])
    for file in aux_files:
        load_ephemeris_fits_to_cache(file)

[codecov]

Codecov Report

Attention: Patch coverage is 92.64706% with 10 lines in your changes missing coverage. Please review.

Project coverage is 76.21%. Comparing base (f6b4a88) to head (d49769b).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
stixpy/product/sources/anc.py	87.09%	4 Missing ⚠️
stixpy/coordinates/transforms.py	92.85%	3 Missing ⚠️
stixpy/utils/table_lru.py	94.73%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #165      +/-   ##
==========================================
+ Coverage   75.50%   76.21%   +0.70%     
==========================================
  Files          32       35       +3     
  Lines        2111     2224     +113     
==========================================
+ Hits         1594     1695     +101     
- Misses        517      529      +12     

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