Accept CCSDS header fields as converter inputs

[tloubrieu-jpl]

This is a small step toward adding converter which calculate and compare the CRC of the packets with the CRC transmitted at the end of the packets.

I wrote a prototype for it in the Europa-Clipper application which uses ccsdspy, but I am not happy with it yet to propose it in the CCSDSpy repository.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.11%. Comparing base (1522816) to head (8e09f86).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #118      +/-   ##
==========================================
+ Coverage   96.05%   96.11%   +0.06%     
==========================================
  Files           7        7              
  Lines         710      721      +11     
==========================================
+ Hits          682      693      +11     
  Misses         28       28              

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[ddasilva]

Thanks @tloubrieu-jpl !