feat(templates): use lines to render smooth template

[shcheklein]

Updates smooth Vega template to partially address iterative/vscode-dvc#3837 and be similar to TB:

Screen.Recording.2023-05-12.at.7.44.32.PM.mov

The thicker line should be the smooth one. Also, don't use point (looks strange after all), use a line with opacity. To solve the issue with a single dot not visible, use additional mark with aggregation that renders a circle only at the end of the plot.

Also cleanups tooltips to include only values (no rev, etc). (we need to do better tooltips, TB style - it's annoying to search for a point every time):

Screen.Recording.2023-05-12.at.7.42.32.PM.mov

Screen.Recording.2023-05-12.at.7.40.38.PM.mov

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.06 🎉

Comparison is base (33eae51) 94.49% compared to head (7ee83b0) 94.55%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #131      +/-   ##
==========================================
+ Coverage   94.49%   94.55%   +0.06%     
==========================================
  Files          19       19              
  Lines         726      735       +9     
  Branches      113      114       +1     
==========================================
+ Hits          686      695       +9     
  Misses         27       27              
  Partials       13       13              

Impacted Files	Coverage Δ
src/dvc_render/vega_templates.py	93.87% <ø> (ø)
src/dvc_render/utils.py	100.00% <100.00%> (ø)
tests/test_table.py	100.00% <100.00%> (ø)
tests/test_vega.py	100.00% <100.00%> (ø)

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[dberenbaum]

The line changes look good!

IMO keeping all the logic for the mark to avoid an empty plot isn't worth it. A linear plot with a single point is kind of meaningless no matter what we show, and TB (and mlflow and wandb AFAIR) are fine to show an empty plot at the start:

Not a blocker, just my take.

[shcheklein]

A linear plot with a single point is kind of meaningless no matter what we show, and TB (and mlflow and wandb AFAIR) are fine to show an empty plot at the start

Merging as is for now. I remember it was a bit confusing for me. Do they also show only if there are two+ epochs?