Build the NUTS kernel with a logprob function

[rlouf]

We currently need to provide a potential function to build the NUTS kernel. However, end users are used to working with logprobs and not potentials so this might be confusing. We thus now require a logpropb function to build the NUTS kernel (it is already the case for the HMC kernel).

Closes #30

[codecov]

Codecov Report

Merging #31 (ce97903) into main (88a4538) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #31   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines          344       345    +1     
  Branches        14        14           
=========================================
+ Hits           344       345    +1     

Impacted Files	Coverage Δ
aehmc/nuts.py	100.00% <100.00%> (ø)

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