NUTS without termination criterion

[callum-kl]

Initial implementation of NUTS but without more complex features (e.g. termination criterion).

• Adds ability to build a binary tree with a single fixed depth.
• Build and merge multiple binary trees of varying depth
• transition! implementation with Multinomial Sampling
• Modifies step! implementation to allow forward or backward in time steps

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.61%. Comparing base (34d4ce2) to head (bb974cb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #33      +/-   ##
==========================================
+ Coverage   89.36%   93.61%   +4.25%     
==========================================
  Files           7        7              
  Lines         141      188      +47     
==========================================
+ Hits          126      176      +50     
+ Misses         15       12       -3     

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[callum-kl]

rename?