fix: MSSSIM and SSIM dist_reduce_fx when reduction=None for distributed training

[rittik9]

What does this PR do?

Fixes issue mentioned in #3159 (comment) also adds test for #3162.

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

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📚 Documentation preview 📚: https://torchmetrics--3166.org.readthedocs.build/en/3166/

[Borda]

can we have a test for it?

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 70%. Comparing base (d3259c0) to head (ab401ea).
⚠️ Report is 77 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #3166    +/-   ##
=======================================
- Coverage      70%     70%    -0%     
=======================================
  Files         364     349    -15     
  Lines       20063   19868   -195     
=======================================
- Hits        14090   13896   -194     
+ Misses       5973    5972     -1     

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[rittik9]

Hi @Borda, altho I can reproduce the issue in my local with the reproducible code sample: #3159 provided. But here with the added test I am unable to reproduce the error in distributed setting. I need some help here to reproduce the issue. Then I can add the fix...

[Borda]

Hi @Borda, altho I can reproduce the issue in my local with the reproducible code sample: #3159 provided. But here with the added test I am unable to reproduce the error in distributed setting. I need some help here to reproduce the issue. Then I can add the fix...

So, you say that the patch resolves the problem, but it is difficult to create a test for it?
In such a case, I trust you and I would merge it so we can think about the test later...

[rittik9]

finally able to reproduce the issue

[rittik9]

Hi @Borda, this one ready for review. I've also added test for #3162.