Add hints for tabular

[kaushikb11]

What does this PR do?

Add type hints for tabular

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[codecov]

Codecov Report

Merging #90 (9692215) into master (841986a) will decrease coverage by 8.54%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #90      +/-   ##
==========================================
- Coverage   86.63%   78.08%   -8.55%     
==========================================
  Files          45       45              
  Lines        1369     1369              
==========================================
- Hits         1186     1069     -117     
- Misses        183      300     +117     

Flag	Coverage Δ
unittests	78.08% <100.00%> (-8.55%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/tabular/classification/data/data.py	84.70% <ø> (ø)
flash/tabular/classification/data/dataset.py	75.75% <100.00%> (ø)
flash/text/seq2seq/core/data.py	30.13% <0.00%> (-54.80%)	⬇️
flash/text/classification/data.py	31.86% <0.00%> (-53.85%)	⬇️
flash/text/classification/model.py	66.66% <0.00%> (-30.31%)	⬇️
flash/text/seq2seq/translation/model.py	55.55% <0.00%> (-16.67%)	⬇️
flash/text/seq2seq/summarization/metric.py	84.48% <0.00%> (-12.07%)	⬇️
flash/text/seq2seq/translation/data.py	76.92% <0.00%> (-7.70%)	⬇️
flash/text/seq2seq/summarization/data.py	76.92% <0.00%> (-7.70%)	⬇️
flash/text/seq2seq/core/model.py	61.90% <0.00%> (-6.35%)	⬇️
... and 2 more

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[Borda]

lgtm, just fix the failing tests