replace [Discrete]Distribution trait for traits for moments and entropy separately

[YeungOnion]

• feat: define new traits Covariance, Entropy, and CentralMoment
• feat!: replace Distribution with new traits for binomial
• feat!: replace Distribution with new traits for Gamma
• feat!: replace Distribution with new traits for uniform
• feat!: replace DiscreteDistribution for new traits for negative binomial
• feat!: replace Distribution for new traits with F-distribution
• feat!: replace Distribution for new traits for laplace
• feat!: replace Distribution for new traits for normal
• feat!: replace Distribution for new traits for multivariate vector distributions

[codecov]

Codecov Report

Attention: Patch coverage is 72.25434% with 192 lines in your changes missing coverage. Please review.

Project coverage is 92.57%. Comparing base (993a4b5) to head (3844e92).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/statistics/traits.rs	11.11%	32 Missing ⚠️
src/distribution/hypergeometric.rs	20.00%	20 Missing ⚠️
src/distribution/fisher_snedecor.rs	33.33%	18 Missing ⚠️
src/distribution/weibull.rs	63.15%	14 Missing ⚠️
src/distribution/bernoulli.rs	43.47%	13 Missing ⚠️
src/distribution/pareto.rs	47.36%	10 Missing ⚠️
src/distribution/students_t.rs	44.44%	10 Missing ⚠️
src/distribution/chi_squared.rs	55.55%	8 Missing ⚠️
src/distribution/erlang.rs	50.00%	8 Missing ⚠️
src/distribution/beta.rs	79.41%	7 Missing ⚠️
... and 18 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #304      +/-   ##
==========================================
- Coverage   93.73%   92.57%   -1.17%     
==========================================
  Files          53       53              
  Lines       12010    12174     +164     
==========================================
+ Hits        11258    11270      +12     
- Misses        752      904     +152     

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[YeungOnion]

@FreezyLemon this removes the statistics::DiscreteDistribution and statistics::Distribution traits.
I'm relying a bit on unimplemented here - was wondering if I should have meaningful associated types for those trait methods as some are unit.

[FreezyLemon]

Looks really good, I like this API.

I'm relying a bit on unimplemented here - was wondering if I should have meaningful associated types for those trait methods as some are unit.

Hm.. good question. Setting the correct type feels right, but might be unexpected for a user because the unimplemented!() macro will only panic at runtime.

Probably better to set it to () for now, and maybe comment that it's unimplemented ("should be f32 but is unimplemented")? Something like that

Edit: The #[deprecated("...")] attribute could also be (mis)used to denote a function as unimplemented. That would create a compile-time warning which should be fairly easy to spot.

[FreezyLemon]

Should probably have a few tests for this

[YeungOnion]

Would be nice to have the Never ! type, but that's not stable. Will do this for now. I'll write out the tests next.

[YeungOnion]

Okay, I'll write the tests for Covariance now, but I realized that I didn't have to find a way to express in associated type if something is unimplemented, I could just separate the traits.

Aside: I learned about ast-grep and it was useful for the rewrite.

[YeungOnion]

I also dropped the sparse trait method from the Covariance trait and renamed the trait to CovarianceMatrix perhaps there's another name more suitable, but the intent was to support various types as if they expressed covariance as an operator and how it acts on states. It felt a little ambiguous across types unlike the dense method.

[YeungOnion]

Not sure what I'm misunderstanding about colorize/whiten and its testing regarding this.
Since square roots of matrices aren't unique, I'm relying on the quadratic forms like seen in distribution functions that have covariance matrices, like in the gaussian $-\frac{1}{2}x^T \Sigma^{-1}x$
This is also how scipy does their tests