Using string instead of Dim

[xadupre]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 52.67490% with 115 lines in your changes missing coverage. Please review.

Project coverage is 70.77%. Comparing base (1eab135) to head (4cfd786).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
onnx_diagnostic/helpers/helper.py	40.35%	102 Missing ⚠️
onnx_diagnostic/torch_models/test_helper.py	66.66%	9 Missing ⚠️
...nx_diagnostic/torch_export_patches/patch_inputs.py	89.47%	2 Missing ⚠️
onnx_diagnostic/export/dynamic_shapes.py	92.85%	1 Missing ⚠️
.../torch_export_patches/onnx_export_serialization.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #58      +/-   ##
==========================================
- Coverage   71.72%   70.77%   -0.95%     
==========================================
  Files          76       76              
  Lines        6408     6583     +175     
==========================================
+ Hits         4596     4659      +63     
- Misses       1812     1924     +112     

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