Adds more robust timer duration parsing

[kylebgorman]

What does this PR do?

Failure to provide the timer duration string (e.g., via --max_time) in the appropriate format currently results in an uninformative IndexError. This uses a simple regex (and the built-in re) for more robust input validation and instead throws a misconfiguration exception.

I experimented with datetime.strptime for this, but it is not well-suited to the job because it is designed for absolute times, not deltas, and therefore does not support the idea of "0 days".

Fixes #19454.

I am submitting as is, but reviewers, feel free to recommend testing.

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📚 Documentation preview 📚: https://pytorch-lightning--19513.org.readthedocs.build/en/19513/

[awaelchli]

@kylebgorman This is already great!

Would you like to try adding a unit test for this?
It would go into the file tests/tests_pytorch/callbacks/test_timer.py. You can use

with pytest.raises(Misconfiguration, match="Expected DD:HH:MM:SS format"):
    Timer(...)

to test your code.

Otherwise I'm happy to help or do it.

[kylebgorman]

I greatly appreciate the suggestions, particularly about wording of the exception. I'll add a unit test shortly.

[awaelchli]

That's great, thanks a lot for adding the test!
Feel free to also add an entry in the "Added" section of the changelog in src/lightning/pytorch/CHANGELOG.md

[kylebgorman]

That's great, thanks a lot for adding the test! Feel free to also add an entry in the "Added" section of the changelog in src/lightning/pytorch/CHANGELOG.md

Done.

[codecov]

Codecov Report

Merging #19513 (f478d73) into master (0f4522c) will decrease coverage by 35%.
The diff coverage is 100%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #19513      +/-   ##
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- Coverage      84%      48%     -35%     
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  Files         450      442       -8     
  Lines       38264    38113     -151     
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- Hits        31996    18444   -13552     
- Misses       6268    19669   +13401