Optimize connected components

[wingertge]

Pull Request Template

Checklist

• Confirmed that run-checks all script has been executed.
• Made sure the book is up to date with changes in this PR.

Changes

Uses NdArray's inner Vec where possible in into_data.
Changes bool_into_data to not force the data to bool, and instead use Backend::BoolElem. Manually converting to bool no longer makes sense when we have an explicit type for boolean elements.
Uses raw pointers for generated code, since bounds checks are proven by nature of the generation algorithm and it's a free speedup.
Removes batch support for connected components since it didn't really make sense, especially for the with_stats version. This matches opencv.

Testing

Passes all tests

[codecov]

Codecov Report

Attention: Patch coverage is 56.21939% with 447 lines in your changes missing coverage. Please review.

Project coverage is 81.73%. Comparing base (2c4c039) to head (5052bc6).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...nents/spaghetti/Spaghetti_last_line_forest_code.rs	5.98%	267 Missing ⚠️
.../cube/connected_components/hardware_accelerated.rs	0.00%	47 Missing ⚠️
...ents/spaghetti/Spaghetti_first_line_forest_code.rs	30.30%	46 Missing ⚠️
...backends/cpu/connected_components/spaghetti/mod.rs	76.85%	25 Missing ⚠️
...nts/spaghetti/Spaghetti_single_line_forest_code.rs	0.00%	24 Missing ⚠️
crates/burn-tensor/src/tensor/element/cast.rs	25.00%	18 Missing ⚠️
crates/burn-vision/src/ops/base.rs	0.00%	10 Missing ⚠️
...sion/src/backends/cube/connected_components/mod.rs	0.00%	4 Missing ⚠️
crates/burn-fusion/src/ops/boolean.rs	91.66%	3 Missing ⚠️
crates/burn-tensor/src/tests/ops/nan.rs	0.00%	2 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2810      +/-   ##
==========================================
+ Coverage   81.69%   81.73%   +0.03%     
==========================================
  Files         851      851              
  Lines      113982   114053      +71     
==========================================
+ Hits        93122    93218      +96     
+ Misses      20860    20835      -25     

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[laggui]

Thanks for making the changes for the bool elem! Pretty much in line with other element types now since it can be backend-specific.