Use truncnorm for bounded Gaussian prior

[DotanGazith]

Using rv_continuous results in an accumulation of the distribution at the upper_bound when sampling.
If not used elsewhere, can remove pint.models.priors.GaussianRV_gen and import of rv_continuous.

[abhisrkckl]

Please add an entry in CHANGELOG-unreleased.md and a test.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.32%. Comparing base (8e414f9) to head (a54bc48).
⚠️ Report is 68 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1995      +/-   ##
==========================================
- Coverage   70.34%   70.32%   -0.02%     
==========================================
  Files         109      109              
  Lines       25652    25745      +93     
  Branches     4081     4106      +25     
==========================================
+ Hits        18044    18105      +61     
- Misses       6453     6473      +20     
- Partials     1155     1167      +12     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.