Add starnet model backbone for tablestructure model

[felixdittrich92]

This PR:

• Add StarNet as backbone for TableCenterNet

• Add DeformConv onnx-exportable version

• Add cor tests & docs

• Add latex required chars to VOCABS

[codecov]

Codecov Report

❌ Patch coverage is 73.88060% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.51%. Comparing base (b4a3c2b) to head (40eb3df).

Files with missing lines	Patch %	Lines
doctr/models/modules/layers/pytorch.py	14.63%	35 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2087      +/-   ##
==========================================
- Coverage   96.94%   96.51%   -0.43%     
==========================================
  Files         157      159       +2     
  Lines        7625     7753     +128     
==========================================
+ Hits         7392     7483      +91     
- Misses        233      270      +37     

Flag	Coverage Δ
unittests	96.51% <73.88%> (-0.43%)	⬇️

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