Lazy load torch

[quentinblampey]

If torch is installed, importing spatialdata will also import torch because of ImageTilesDataset.

This PR aims to speed up the import by making the import of torch lazy.

It's a little bit tricky to keep all the dosctrings + auto-completion. For now, it seems the auto-completion is working fine for the instances, but not the __init__ docstrings.

If you think this PR seems interesting, I can work on fixing the docstrings, else we can just close it

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.15%. Comparing base (53b9438) to head (360fdc4).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1027      +/-   ##
==========================================
+ Coverage   92.11%   92.15%   +0.03%     
==========================================
  Files          49       49              
  Lines        7537     7542       +5     
==========================================
+ Hits         6943     6950       +7     
+ Misses        594      592       -2     

Files with missing lines	Coverage Δ
src/spatialdata/dataloader/__init__.py	100.00% <100.00%> (+50.00%)	⬆️

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[Zethson]

Very much interesting and we did something similar for anndata: scverse/anndata#1959

Feel free to consider our approach that we used there.

[quentinblampey]

Oh thanks @Zethson, your approach seems much better and very straightforward, I'll try that!

[quentinblampey]

I made the change, WDYT @Zethson?

[Zethson]

Looks fine but I'll leave this PR up to the maintainers now.

[LucaMarconato]

LGTM thanks a lot!