Newmetric: Negative predictive value

[SkafteNicki]

What does this PR do?

Fixes #2415

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• Did you make sure to update the docs?
• Did you write any new necessary tests?

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📚 Documentation preview 📚: https://torchmetrics--2433.org.readthedocs.build/en/2433/

[Asunatan]

Thank you for your team's significant contribution to calculating negative predictive value (NPV) as a new classification metric. This work can reduce the computational burden on clinical doctors.

[codecov]

Codecov Report

Attention: Patch coverage is 51.81818% with 53 lines in your changes missing coverage. Please review.

Project coverage is 41%. Comparing base (76c502b) to head (eda9e87).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #2433     +/-   ##
========================================
- Coverage      69%     41%    -28%     
========================================
  Files         328     344     +16     
  Lines       18525   18823    +298     
========================================
- Hits        12737    7642   -5095     
- Misses       5788   11181   +5393     

[lantiga]

LGTM, just a few nits on the docstrings