More moments

[michaelosthege]

This adds get_moment implementations and tests them more thoroughly.

[codecov]

Codecov Report

Merging #5025 (116ae6b) into main (37ba9a3) will decrease coverage by 0.04%.
The diff coverage is 61.76%.

❗ Current head 116ae6b differs from pull request most recent head b9001f7. Consider uploading reports for the commit b9001f7 to get more accurate results

@@            Coverage Diff             @@
##             main    #5025      +/-   ##
==========================================
- Coverage   77.85%   77.81%   -0.05%     
==========================================
  Files         128      128              
  Lines       24349    24380      +31     
==========================================
+ Hits        18958    18972      +14     
- Misses       5391     5408      +17     

Impacted Files	Coverage Δ
pymc/distributions/distribution.py	87.16% <0.00%> (ø)
pymc/distributions/discrete.py	98.34% <33.33%> (-0.66%)	⬇️
pymc/distributions/continuous.py	95.93% <62.50%> (-0.34%)	⬇️
pymc/tests/test_initvals.py	91.46% <68.18%> (-8.54%)	⬇️
pymc/parallel_sampling.py	86.28% <0.00%> (-1.01%)	⬇️
pymc/step_methods/hmc/nuts.py	96.87% <0.00%> (-0.63%)	⬇️
pymc/step_methods/metropolis.py	83.48% <0.00%> (-0.23%)	⬇️