Convert between LPS/RAS coordinate systems

[kaitj]

Proposed changes
Adds a method that takes in one AfidSet in either "LPS" or "RAS" coordinate system and returns a new AfidSet in the opposite coordinate system. Open to moving this as a method of AfidSet, but opted for a separate function as a first pass.

One thing that needs to be checked is if the coordinates need to be in a certain system to work with the affine pulled via nibabel in the world / voxel functions, but that should be done in a separate PR if an update is needed.

Types of changes
What types of changes does your code introduce? Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other (if none of the other choices apply)

Checklist
Put an x in the boxes that apply. You can also fill these out after creating the PR. If you are unsure about any of the choices, don't hesitate to ask!

• Changes have been tested to ensure that fix is effective or that a feature works.
• Changes pass the unit tests
• Code has been run through the poe quality task
• I have included necessary documentation or comments (as necessary)
• Any dependent changes have been merged and published

Notes
All PRs will undergo the unit testing before being reviewed. You may be requested to explain or make additional changes before the PR is accepted.

[codecov]

Codecov Report

Merging #32 (78c975c) into main (d1ba3af) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #32   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          503       529   +26     
=========================================
+ Hits           503       529   +26     

Components	Coverage Δ
afids_utils/afids.py	∅ <ø> (∅)
afids_utils/ext	100.00% <ø> (ø)
afids_utils/transforms.py	100.00% <100.00%> (ø)

📢 Have feedback on the report? [Share it here](https://about.codecov.io/codecov-pr-comment-feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=afids).

[tkkuehn]

Mostly looks good, just a few nitpicky style comments

[kaitj]

Implemented the suggested changes and also took the opportunity to update the docs (minor update includes adding AfidVoxel to the documentation)