Adds function to plot onnx model as graphs

[xadupre]

No description provided.

[codecov-commenter]

Codecov Report

Attention: 36 lines in your changes are missing coverage. Please review.

Comparison is base (7895c27) 82.43% compared to head (2e02703) 82.22%.

Files	Patch %	Lines
onnx_array_api/plotting/graphviz_helper.py	65.62%	33 Missing ⚠️
onnx_array_api/ext_test_case.py	70.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
- Coverage   82.43%   82.22%   -0.21%     
==========================================
  Files          54       55       +1     
  Lines        7291     7397     +106     
==========================================
+ Hits         6010     6082      +72     
- Misses       1281     1315      +34     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.