add fusion matmul optimization i64 support

[tzemanovic]

Pull Request Template

Checklist

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

Changes

Adds i64 support to matmul fusion.

I ran into the Unsupported precision catch-all case with i64. It seems that simply adding a case to handle this works, at least in my external work. One thing I'm not sure about if the row_count for FusedMatmulSelector::OrderedDoubleBuffering on line 506 in this file should also be updated to handle this precision?

Testing

Only tested externally in private code. I'd be happy to add some tests here with some guidance

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 64.75%. Comparing base (3fc8243) to head (c83418c).

Files with missing lines	Patch %	Lines
...ates/burn-cubecl-fusion/src/matmul/optimization.rs	0.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project check has failed because the head coverage (64.75%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3950   +/-   ##
=======================================
  Coverage   64.75%   64.75%           
=======================================
  Files        1178     1178           
  Lines      140098   140099    +1     
=======================================
+ Hits        90720    90721    +1     
  Misses      49378    49378           

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[nathanielsimard]

It's not just i64, but all int types that are not supported in fusion. This can be fixed by extending the enum match case.