Remove NoDistribution and enable .dist API for Simulator and DensityDist

[ricardoV94]

What is this PR about?

The NoDistribution was used originally for Simulator, to allow RVs in the graph, but that hasn't been needed for sometime.

Besides removing that class, this PR also implements the .dist API for DensityDist and Simulator so that they behave more like other Distributions. The only difference is that a class_name is required as these classes create new types dynamically.

Closes #6031

Checklist

• Explain important implementation details 👆
• Make sure that the pre-commit linting/style checks pass.
• Link relevant issues (preferably in nice commit messages)
• Are the changes covered by tests and docstrings?
• Fill out the short summary sections 👇

Major / Breaking Changes

• Remove NoDistribution in favor of Distribution

Bugfixes / New features

• DensityDist and Simulator can now be created via the .dist API

Docs / Maintenance

• ...

[codecov]

Codecov Report

Merging #6110 (808b0f9) into main (c6e5a92) will increase coverage by 8.65%.
The diff coverage is 11.89%.

@@            Coverage Diff             @@
##             main    #6110      +/-   ##
==========================================
+ Coverage   59.74%   68.39%   +8.65%     
==========================================
  Files          86       86              
  Lines       17848    18027     +179     
==========================================
+ Hits        10663    12330    +1667     
+ Misses       7185     5697    -1488     

Impacted Files	Coverage Δ
pymc/distributions/__init__.py	100.00% <ø> (ø)
pymc/tests/distributions/test_distribution.py	0.00% <0.00%> (ø)
pymc/tests/distributions/test_simulator.py	0.00% <0.00%> (ø)
pymc/distributions/simulator.py	34.04% <50.00%> (-53.46%)	⬇️
pymc/distributions/distribution.py	89.77% <86.66%> (+1.61%)	⬆️
pymc/gp/util.py	96.55% <100.00%> (ø)
pymc/smc/smc.py	18.89% <0.00%> (-77.56%)	⬇️
pymc/smc/sample_smc.py	16.77% <0.00%> (-66.45%)	⬇️
pymc/data.py	67.88% <0.00%> (-12.20%)	⬇️
... and 31 more