Jit support

[ethanwharris]

What does this PR do?

Makes flash tasks jittable where possible:
Todo:

• Image classification
• object detection
• style transfer
• embedding
• tabular
• template task
• text classification
• translation
• summarisation
• video
• docs

Fixes #386

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• Did you write any new necessary tests? [not needed for typos/docs]
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[codecov]

Codecov Report

Merging #389 (9540acc) into master (a047330) will increase coverage by 0.33%.
The diff coverage is 90.62%.

@@            Coverage Diff             @@
##           master     #389      +/-   ##
==========================================
+ Coverage   89.45%   89.79%   +0.33%     
==========================================
  Files          80       80              
  Lines        4192     4203      +11     
==========================================
+ Hits         3750     3774      +24     
+ Misses        442      429      -13     

Flag	Coverage Δ
gpu	?
pytest	?
unittests	89.79% <90.62%> (+0.33%)	⬆️

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

Impacted Files	Coverage Δ
flash/image/classification/model.py	86.36% <ø> (-0.88%)	⬇️
flash/image/detection/model.py	80.51% <60.00%> (+0.51%)	⬆️
flash/text/classification/model.py	90.00% <80.00%> (+0.52%)	⬆️
flash/core/data/process.py	88.83% <100.00%> (-6.10%)	⬇️
flash/core/model.py	87.54% <100.00%> (+0.20%)	⬆️
flash/image/embedding/model.py	81.03% <100.00%> (+40.68%)	⬆️
flash/image/segmentation/model.py	86.88% <100.00%> (ø)
flash/tabular/classification/model.py	83.72% <100.00%> (+1.66%)	⬆️
flash/image/detection/data.py	95.16% <0.00%> (-1.62%)	⬇️
... and 9 more

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[tchaton]

LGMT !