feat: adding annCollection dataloader

[ori-kron-wis]

based on https://github.com/scverse/scvi-tools/issues/3018

[codecov[bot]]

Codecov Report

:x: Patch coverage is 87.71930% with 7 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 78.90%. Comparing base (bb48fa7) to head (b6239a4). :warning: Report is 63 commits behind head on main.

Files with missing lines	Patch %	Lines
src/scvi/dataloaders/_anncollection.py	87.50%	7 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3362      +/-   ##
==========================================
+ Coverage   78.87%   78.90%   +0.02%     
==========================================
  Files         208      209       +1     
  Lines       18925    18982      +57     
==========================================
+ Hits        14927    14977      +50     
- Misses       3998     4005       +7     

Files with missing lines	Coverage Δ
src/scvi/dataloaders/__init__.py	100.00% <100.00%> (ø)
src/scvi/dataloaders/_anncollection.py	87.50% <87.50%> (ø)

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[canergen]

There seems to be more legacy. Can your remove all and tag me? I can have another look then.

[lumberbot-app[bot]]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 1.3.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 8e223628ffb607bb26bfb58659af09ba4df7d412

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #3362: feat: adding annCollection dataloader'

4. Push to a named branch:

git push YOURFORK 1.3.x:auto-backport-of-pr-3362-on-1.3.x

5. Create a PR against branch 1.3.x, I would have named this PR:

"Backport PR #3362 on branch 1.3.x (feat: adding annCollection dataloader)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.