Fix multi-GPU support for post-processor

[djdameln]

📝 Description

• This fixes the performance difference between single- and multi-gpu setups.

Causes of the problem:

• Failure to correctly reduce the internal metric states of the MinMax metrics between devices.
  • Solution: Set dist_reduce_fx to appropriate method when defining states in MinMax value.
• Wrong use of metric state in F1AdaptiveThreshold (metric states should not be used to store final value).
  • Solution: Remove computed value as internal state and register the value as a buffer in the PostProcessor instead.

✨ Changes

Select what type of change your PR is:

• 🐞 Bug fix (non-breaking change which fixes an issue)
• 🔨 Refactor (non-breaking change which refactors the code base)
• 🚀 New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔒 Security update

✅ Checklist

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• 📋 I have summarized my changes in the CHANGELOG and followed the guidelines for my type of change (skip for minor changes, documentation updates, and test enhancements).
• 📚 I have made the necessary updates to the documentation (if applicable).
• 🧪 I have written tests that support my changes and prove that my fix is effective or my feature works (if applicable).

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[samet-akcay]

thanks for the fix!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.62%. Comparing base (084331d) to head (7d3a8ab).
Report is 1 commits behind head on main.

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HEAD has 1 upload less than BASE

Flag	BASE (084331d)	HEAD (7d3a8ab)
	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2499       +/-   ##
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- Coverage   78.94%   64.62%   -14.33%     
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  Files         311      311               
  Lines       13197    13183       -14     
===========================================
- Hits        10419     8519     -1900     
- Misses       2778     4664     +1886     

Flag	Coverage Δ
unit_py3.10	64.62% <100.00%> (?)

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