Load AnnLoader lazily to avoid torch imports when not requested

[Zethson]

• Closes Import torch lazily #1950
• Tests added: No because we don't have have a matrix with torch. Happy to add something if desired.
• Release note added (or unnecessary)

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.03%. Comparing base (089ed92) to head (631aafa).

Files with missing lines	Patch %	Lines
src/anndata/experimental/__init__.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1959      +/-   ##
==========================================
- Coverage   87.13%   85.03%   -2.10%     
==========================================
  Files          47       47              
  Lines        6848     6850       +2     
==========================================
- Hits         5967     5825     -142     
- Misses        881     1025     +144     

Files with missing lines	Coverage Δ
src/anndata/experimental/__init__.py	88.23% <33.33%> (-11.77%)	⬇️

... and 7 files with indirect coverage changes

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[flying-sheep]

this (without the -) belongs into a file called 1959.performance.md that you create using hatch towncrier:create

0.12.0rc1 is already released and its release notes are complete.