New wrapper FeatureShare

[SkafteNicki]

What does this PR do?

Fixes #2099
Introduces a new wrapper FeatureShare that is intended to be used with metrics that uses some underlying neural network to do their calculation. As pointed out in the issue it is a waste of memory that the same network that can be shared between networks gets initialized multiple times and that the computations in not reused.

Work in progress...

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• Did you write any new necessary tests?

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📚 Documentation preview 📚: https://torchmetrics--2120.org.readthedocs.build/en/2120/

[codecov]

Codecov Report

Merging #2120 (49b42e3) into master (7543641) will decrease coverage by 40%.
Report is 1 commits behind head on master.
The diff coverage is 76%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #2120     +/-   ##
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- Coverage      87%     47%    -40%     
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  Files         300     303      +3     
  Lines       16971   17059     +88     
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- Hits        14737    7991   -6746     
- Misses       2234    9068   +6834