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

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.12%. Comparing base (53b9438) to head (557f53b).

Files with missing lines	Patch %	Lines
src/spatialdata/dataloader/__init__.py	83.33%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1027   +/-   ##
=======================================
  Coverage   92.11%   92.12%           
=======================================
  Files          49       49           
  Lines        7537     7545    +8     
=======================================
+ Hits         6943     6951    +8     
  Misses        594      594           

Files with missing lines	Coverage Δ
src/spatialdata/dataloader/__init__.py	83.33% <83.33%> (+33.33%)	⬆️

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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!