dvclive.log Refactor

[daavoo]

• ❗ I have followed the Contributing to DVCLive guide.

• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here.

Included some refactor (sorry for the number of changes 🙏) which wasn't strictly necessary to address the changes but I think would help in upcoming changes:

• Added data module.
• Extracted make_html to dvclive.dvc.
• Extracted new method make_summary.

Added the following changes :

• summary is now generated in dvclive.log. Closes logger: log to summary first, then to logs #145
• dvclive.log raises a new AlreadyLoggedError if called with the same metric and step . Closes dvclive.log: Remove the implicit next_step call . #162
• make_html and make_checkpoint are now called in dvclive.set_step. dvclive.next_step is now an alias for

self.set_step(self.get_step() + 1)

This should fulfill the 3 points listed in #157 (comment), considering that checkpoints would be properly handled by DVC.

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I'm starting to think that make_checkpoints, make_html, and make_summary could be extracted to explicit public methods. Even though it might increase the complexity of the API, it should drive users to one of:

a) Use our integrations.
b) This is our canonical workflow but feel free to alter it, there are no side effects.

[codecov-commenter]

Codecov Report

Merging #164 (8c17d63) into master (df9ed2b) will increase coverage by 0.41%.
The diff coverage is 96.42%.

@@            Coverage Diff             @@
##           master     #164      +/-   ##
==========================================
+ Coverage   91.91%   92.32%   +0.41%     
==========================================
  Files          15       17       +2     
  Lines         371      417      +46     
==========================================
+ Hits          341      385      +44     
- Misses         30       32       +2     

Impacted Files	Coverage Δ
dvclive/utils.py	100.00% <ø> (ø)
dvclive/data/base.py	90.90% <90.90%> (ø)
dvclive/metrics.py	97.91% <96.87%> (+0.72%)	⬆️
dvclive/data/__init__.py	100.00% <100.00%> (ø)
dvclive/data/scalar.py	100.00% <100.00%> (ø)
dvclive/dvc.py	66.66% <100.00%> (+4.76%)	⬆️
dvclive/error.py	95.65% <100.00%> (+1.20%)	⬆️

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[pared]

LGTM, I would consider creating some minor test (or updating test_nested_logging) with a check that verifies that first log updates summary.