[io] Expose the table structure cell scores on TableCell

[felixdittrich92]

This PR:

• Add objectness_score to each TableCell
• Update API
• Add cor tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.55%. Comparing base (fac9585) to head (ef96318).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2165   +/-   ##
=======================================
  Coverage   97.54%   97.55%           
=======================================
  Files         170      170           
  Lines       10665    10667    +2     
=======================================
+ Hits        10403    10406    +3     
+ Misses        262      261    -1     

Flag	Coverage Δ
unittests	97.55% <100.00%> (+<0.01%)	⬆️

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