Bugfixes for SWIFTGalaxies

[kyleaoman]

There was a bug likely introduced in #72 causing the "data server" in the SWIFTGalaxies iterator to mask the data arrays used while evaluating the mask for bound particles. This leads to a crash if a second galaxy uses the same "data server", i.e. lives in the same region as the masked data has an unexpected shape the next time it is accessed to evaluate the mask for the next galaxy. This has been fixed - thanks to Anna Durant for spotting that there was a problem.

There was also an issue when exactly 2 regions were being iterated over. There is an array used internally that has shape (1, N, M-1) where M is the number of regions. This array was then squeezed with the intention of dropping the dimension with size 1, but also removed the M-1 dimension when M=2. The axis that the squeeze should operate on is now specified explicitly.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5b3f260) to head (a61093e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #77   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            7         7           
  Lines         2294      2297    +3     
  Branches       257       260    +3     
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+ Hits          2294      2297    +3     

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