Fixes and improvements to plot_trace_dist

[OriolAbril]

closes #28 and closes #29.

Makes plot_trace_dist work with bokeh and with all combinations of compact and combined (also testing all 4 cases). In addition it ensures it supports sample_dims="sample" (changes also done for plot_trace).

It still needs more work on docs and rebasing on top of #35 to make it work with the neutral element concept, which could be challenging for combined=True

---

📚 Documentation preview 📚: https://arviz-plots--36.org.readthedocs.build/en/36/

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.95745% with 33 lines in your changes are missing coverage. Please review.

Project coverage is 84.53%. Comparing base (2bdfa18) to head (da292db).

Files	Patch %	Lines
src/arviz_plots/plots/tracedistplot.py	91.07%	10 Missing :warning:
src/arviz_plots/visuals/__init__.py	72.72%	9 Missing :warning:
src/arviz_plots/backend/bokeh/__init__.py	88.63%	5 Missing :warning:
src/arviz_plots/plots/utils.py	61.53%	5 Missing :warning:
src/arviz_plots/backend/matplotlib/__init__.py	80.00%	2 Missing :warning:
src/arviz_plots/plots/traceplot.py	90.47%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #36 +/- ## ========================================== + Coverage 76.82% 84.53% +7.70% ========================================== Files 15 15 Lines 1299 1448 +149 ========================================== + Hits 998 1224 +226 + Misses 301 224 -77 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.