Handle autofluorescence channels and pass through unknown image types

[MSHelm]

Hi everyone,

this fixes #367

I added a dedicated entry for autofluorescence channels to IMAGETYPE_DICT. In addition to future proof this, the parser now passes through unknown image types that are not in the dictionary.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.85%. Comparing base (d13a407) to head (7c0b3cd).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #368   +/-   ##
=======================================
  Coverage   61.85%   61.85%           
=======================================
  Files          26       26           
  Lines        3138     3138           
=======================================
  Hits         1941     1941           
  Misses       1197     1197           

Files with missing lines	Coverage Δ
src/spatialdata_io/readers/macsima.py	93.66% <100.00%> (ø)

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[MSHelm]

Small bump for this PR @LucaMarconato if there is anything that you need in addition, let me know.