Conv Transpose: migration + decent speedup

[louisfd]

Conv transpose 2d kernel for #1422

It was the last of the kernel i had to migrate, so
Fix #1422

Also I spent a bit more time on this kernel because it was notoriously slow.
I sped it up by a factor that scales (not linearly, maybe square root or something) with the kernel size.
Benchmark for conv transpose is added as well.
For instance on my machine, with 8x8 kernel, time decreased from 524ms to 44ms.

[codecov]

Codecov Report

Attention: Patch coverage is 99.70149% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 86.35%. Comparing base (5bac300) to head (186dd66).
Report is 8 commits behind head on main.

Files	Patch %	Lines
...rates/burn-jit/src/kernel/conv/conv_transpose2d.rs	99.70%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1541      +/-   ##
==========================================
+ Coverage   86.19%   86.35%   +0.16%     
==========================================
  Files         673      682       +9     
  Lines       77545    78151     +606     
==========================================
+ Hits        66837    67486     +649     
+ Misses      10708    10665      -43     

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