Set custom tooltip for plotly and other fixes

[aloctavodia]

closes #318

• Customize tooltips to improve readability: 1) use two significant digits, 2) y value in a new line
• Fix tooltip for (sqrt transformation) rootogram, now correctly shows the values for the data in the original scale.
• remove borders from hspan and vspan
• fix missing band in plot_compare when using plotly backend.

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📚 Documentation preview 📚: https://arviz-plots--323.org.readthedocs.build/en/323/

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.03%. Comparing base (c6c4f2f) to head (afcfc69).

Files with missing lines	Patch %	Lines
src/arviz_plots/backend/plotly/__init__.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #323      +/-   ##
==========================================
- Coverage   88.07%   88.03%   -0.05%     
==========================================
  Files          46       46              
  Lines        5659     5673      +14     
==========================================
+ Hits         4984     4994      +10     
- Misses        675      679       +4     

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