* wip
* prototype custom predicates 1b
* feat: implement custom pred recursion
* files reorg, add github CI for rustfmt checks
* start sparsemerkletree. impl add_leaf method, initial Leaf & Intermediate types with methods
* mt: add hash computation of all the nodes in the tree, add method to print the tree to visualize it as a graphviz
* mt: add (till the leaf) method which is used by get,contains,prove methods
* mt: add verify (of inclusion) method
* mt: update 'down' method to reuse siblings, update get,contains,prove methods (the three use 'down' under the hood)
* Add nonexistence proofs and iterator
* Add iterator test
* migrate usage of old merkletree to the new merkletree impl in POD2 code
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Co-authored-by: Eduard S. <eduardsanou@posteo.net>
Co-authored-by: Ahmad <root@ahmadafuni.com>
