integrations: lightning: migrate to simpler model

[pared]

• ❗ 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.

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[codecov-commenter]

Codecov Report

Base: 93.28% // Head: 94.98% // Increases project coverage by +1.69% 🎉

Coverage data is based on head (1bed258) compared to base (d633bfa).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #319      +/-   ##
==========================================
+ Coverage   93.28%   94.98%   +1.69%     
==========================================
  Files          36       36              
  Lines        1727     1734       +7     
  Branches      161      161              
==========================================
+ Hits         1611     1647      +36     
+ Misses         93       64      -29     
  Partials       23       23              

Impacted Files	Coverage Δ
tests/test_lightning.py	95.58% <100.00%> (+0.50%)	⬆️
src/dvclive/lgbm.py	100.00% <0.00%> (+46.66%)	⬆️
tests/test_lgbm.py	100.00% <0.00%> (+48.88%)	⬆️

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