feat: support online eval during score

[senwu]

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Checklist

• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have updated the CHANGELOG.rst accordingly.

[codecov]

Codecov Report

Merging #122 (47486c1) into main (a61b333) will decrease coverage by 3.15%.
Report is 1 commits behind head on main.
The diff coverage is 44.13%.

❗ Current head 47486c1 differs from pull request most recent head 3dc854d. Consider uploading reports for the commit 3dc854d to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #122      +/-   ##
==========================================
- Coverage   92.14%   88.99%   -3.15%     
==========================================
  Files          40       40              
  Lines        2024     2145     +121     
  Branches      456      503      +47     
==========================================
+ Hits         1865     1909      +44     
- Misses         94      169      +75     
- Partials       65       67       +2     

Flag	Coverage Δ
unittests	88.99% <44.13%> (-3.15%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
src/emmental/model.py	76.54% <22.85%> (-17.25%)	⬇️
src/emmental/learner.py	78.75% <100.00%> (+0.42%)	⬆️
src/emmental/meta.py	84.46% <100.00%> (ø)
src/emmental/metrics/accuracy.py	100.00% <100.00%> (ø)
src/emmental/metrics/accuracy_f1.py	100.00% <100.00%> (ø)
src/emmental/metrics/fbeta.py	100.00% <100.00%> (ø)
src/emmental/metrics/matthews_correlation.py	100.00% <100.00%> (ø)
src/emmental/metrics/mean_squared_error.py	100.00% <100.00%> (ø)
src/emmental/metrics/pearson_correlation.py	100.00% <100.00%> (ø)
src/emmental/metrics/pearson_spearman.py	100.00% <100.00%> (ø)
... and 6 more