feat: Added box coord clipping and target validation for detection tasks

[fg-mindee]

This PR introduces the following modifications:

• added box coord clipping to avoid rounding errors in detection datasets
• added target validation for detection models to avoid silent failures
• added unittests for target validation

Any feedback is welcome!

[codecov]

Codecov Report

Merging #355 (d9ab964) into main (9f7edcd) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #355   +/-   ##
=======================================
  Coverage   96.09%   96.10%           
=======================================
  Files          83       83           
  Lines        3404     3412    +8     
=======================================
+ Hits         3271     3279    +8     
  Misses        133      133           

Flag	Coverage Δ
unittests	96.10% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
doctr/datasets/detection.py	96.87% <100.00%> (ø)
...dels/detection/differentiable_binarization/base.py	91.92% <100.00%> (+0.20%)	⬆️
doctr/models/detection/linknet/base.py	88.31% <100.00%> (+0.64%)	⬆️

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[charlesmindee]

Thanks!