Docs for volume preserving attention

[benedict-96]

Added docs for VolumePreservingAttention and fixed some bits.

1. Added a tutorial on VolumePreservingAttention.
2. Expanded the docs on the attention mechanism.
3. Added a test for the cpu inverse in test/kernels/tensor_inverse.jl

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 64.30%. Comparing base (b075906) to head (8a4ddbe).

Files	Patch %	Lines
src/layers/resnet.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #134      +/-   ##
==========================================
+ Coverage   63.69%   64.30%   +0.60%     
==========================================
  Files         117      117              
  Lines        3314     3314              
==========================================
+ Hits         2111     2131      +20     
+ Misses       1203     1183      -20     

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