Adding simple and action distributions

[will-maclean]

For #32. Need both simple distributions and action distributions.

Simple Distributions

• [x] (trait)
• [ ] Uniform
• [x] Normal
• [ ] Categorical
• [ ] Bernoulli

Action Distribution (https://github.com/DLR-RM/stable-baselines3/blob/master/stable_baselines3/common/distributions.py)

• [ ] (trait)
• [x] DiagGaussianDistribution
• [ ] SquashedDiagGaussianDistribution
• [ ] CategoricalDistribution
• [ ] MultiCategoricalDistribution
• [ ] BernoulliDistribution
• [ ] StateDependentNoiseDistribution
• [ ] TanhBijector

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.06584% with 29 lines in your changes missing coverage. Please review.

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Files	Coverage Δ
src/common/distributions/distribution.rs	100.00% <100.00%> (ø)
src/common/utils/mod.rs	98.43% <ø> (ø)
src/common/utils/modules.rs	98.18% <98.18%> (ø)
src/common/distributions/normal.rs	94.94% <94.94%> (ø)
src/common/distributions/action_distribution.rs	86.30% <86.30%> (ø)
src/common/distributions/exp_family.rs	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

[will-maclean]

Going to merge this into main so it can be used as is now, but will convert the remaining distributions to an issue