Skip building bib_data if files are older than config time (for mkdocs serve)

[mdbenito]

This PR is a continuation to #238.

• It uses on_startup() to avoid unloading the plugin when using mkdocs serve.
• It avoids rendering the bibtex for all references during on_config() by storing the time() of the first run, then checking the timestamps of the bibtex files passed by the user. If any file is newer all refs are read again.

The speedup is only noticeable after merging #238, but with both PRs together, our re-build using mkdocs serve goes from ~41secs to ~25 secs, or a 40% total reduction in build time. This makes working on documentation much nicer :)

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 96.20%. Comparing base (1496fab) to head (696189d).
Report is 4 commits behind head on main.

Files	Patch %	Lines
src/mkdocs_bibtex/plugin.py	55.55%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #240      +/-   ##
==========================================
- Coverage   97.97%   96.20%   -1.78%     
==========================================
  Files           3        3              
  Lines         198      211      +13     
==========================================
+ Hits          194      203       +9     
- Misses          4        8       +4     

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[mdbenito]

@shyamd I see the errors. Sorry about that. I'll look into it and get back to you

[shyamd]

Thanks for all these performance improvements and no worries on the failing tests. Took me awhile to turn on tests for your PRs.

[shyamd]

I re-named the attribute that you used for holding the last config time. The fact that it wasn't throwing an AttributeError tells me that mkdocs was already using it. This new attribute throws an AttributeError if you don't use the hasattr guard, which is what we'd hope.

[shyamd]

Thanks for all these performance improvements. Next minor version bump will include them.

[mdbenito]

My pleasure. Thank you for the plugin!