[WIP] MicrographSource/Image updates

[garrettwrong]

Fix MicrographSource so it can load and operate on EMPIAR experimental data (eg 10061). These datasets often have rectangular shapes.

[garrettwrong]

After a few attempts I was able to get this down to a somewhat more reasonable change set. I've made a few other things (migrated things I saw towards classmethods) a bit more consistent while I was in there in case more surgery is required down the road.

I still need to hit the filtering methods so that CTF can be applied to these rectangles. etc.

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 10 lines in your changes missing coverage. Please review.

Project coverage is 90.57%. Comparing base (c255119) to head (e35b9a5).

Files with missing lines	Patch %	Lines
src/aspire/image/image.py	75.00%	5 Missing ⚠️
src/aspire/source/micrograph.py	73.68%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1288      +/-   ##
===========================================
- Coverage    90.60%   90.57%   -0.04%     
===========================================
  Files          132      132              
  Lines        14181    14202      +21     
===========================================
+ Hits         12849    12863      +14     
- Misses        1332     1339       +7     

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