added indexed categorical layer evaluation

[gengala]

as per title.

[codecov]

Codecov Report

Attention: Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review.

Project coverage is 68.18%. Comparing base (fee7960) to head (fe1d8a6).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
cirkit/backend/torch/layers/input.py	44.44%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #313      +/-   ##
==========================================
- Coverage   68.26%   68.18%   -0.09%     
==========================================
  Files          51       51              
  Lines        5360     5368       +8     
  Branches      613      616       +3     
==========================================
+ Hits         3659     3660       +1     
- Misses       1486     1492       +6     
- Partials      215      216       +1     

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[loreloc]

Thank you! Please run the automatic formatter black (see the instructions in README.md). Also, better to avoid unnecessary logic in inference methods. You can cache the result of the if len(torch.unique(self.scope_idx)) > 4096 or self.num_categories > 256 in a boolean value in the init method.