Rat SPN structures

[khosravipasha]

Allows to make RAT-spn structures in Juice

[khosravipasha]

Few changes that might want to do:

• In the leaves currently doing fully_factorized_circuit which might have more than a few variables, leads to having Mult nodes with many children, might want to replace with equivalent fully factorized but only with 2 children per Mult node.

[codecov]

Codecov Report

Merging #92 (17e63c4) into master (8b45db2) will decrease coverage by 0.82%.
The diff coverage is 97.56%.

@@            Coverage Diff             @@
##           master      #92      +/-   ##
==========================================
- Coverage   70.31%   69.49%   -0.83%     
==========================================
  Files          38       38              
  Lines        2850     2993     +143     
==========================================
+ Hits         2004     2080      +76     
- Misses        846      913      +67     

Impacted Files	Coverage Δ
src/ProbabilisticCircuits.jl	100.00% <ø> (ø)
src/structurelearner/rat_spn.jl	97.40% <97.40%> (ø)
src/plain_prob_nodes.jl	100.00% <100.00%> (ø)
src/gradient_based_learning.jl	45.40% <0.00%> (-16.81%)	⬇️
src/queries/marginal_flow.jl	53.15% <0.00%> (-3.59%)	⬇️
src/queries/sample.jl	45.45% <0.00%> (-0.55%)	⬇️
src/Utils/Utils.jl
src/Utils/misc.jl	41.33% <0.00%> (+0.54%)	⬆️

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