Convert progress bar metrics to float

[carmocca]

What does this PR do?

Fixes #5481

### TODO:
- Separate train/val/test metrics
- callback_metrics should copy the data as is, not as a reference from progress_bar_metrics. This way, each MetricHolder is free to make their own conversions without affecting other parts.

edit: leaving refactor out of this PR

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[codecov]

Codecov Report

Merging #5692 (f38d7cb) into release/1.2-dev (a028171) will decrease coverage by 44%.
The diff coverage is 95%.

@@                Coverage Diff                @@
##           release/1.2-dev   #5692     +/-   ##
=================================================
- Coverage               88%     44%    -44%     
=================================================
  Files                  181     181             
  Lines                12964   12796    -168     
=================================================
- Hits                 11462    5632   -5830     
- Misses                1502    7164   +5662     

[Borda]

@carmocca is it still WIP or ready to go? :]

[carmocca]

So I planned to include a larger refactor here. I think i'll commit the one-line fix to master and work on the refactor here.

edit: Nevermind, MetricHolder is not in master

[Borda]

So I planned to include a larger refactor here. I think i'll commit the one-line fix to master and work on the refactor here.

I would rather have multiple smaller refactors, it is easier to review :]

[awaelchli]

Just one request: could we move the test to the logging tests? Because the conversion doesn't happen in the progress bar therefore I propose to move this test outside the progress bar unit tests.

[Borda]

pls see #5692 (review)

[carmocca]

Just one request: could we move the test to the logging tests? Because the conversion doesn't happen in the progress bar therefore I propose to move this test outside the progress bar unit tests.

I disagree. The purpose of the test is to check that the progress bar correctly displays the number as a float, not a tensor. The fact that the changed code is in the logger connector is independent to the problem this PR is solving. If the logger connector was completely replaced by a different abstraction, I still want to make sure the progress bar does not change.

Tell me if you still want me to change it.

[awaelchli]

I am not convinced with your argument but it's ok I don't want to block. If we change our mind we can move the test later.