jmt(ics23): add proptests for each nonexistence setups

[erwanor]

The ICS23 adjacency calculation can happen over three types of configurations reflected in ics23::NonExistenceProof, indeed, either the queried key has:

• only a right neighbor (leftmost key)
• only a left neighbor (rightmost key)
• or both

As part of our #103 effort, we should add prop tests that take advantage of the TransparentHasher to test each configurations with arbitrary depth.

          One nit, inline, and a thought: can we capture the essence of these unit tests as a proptest?

Originally posted by @plaidfinch in #100 (review)

[erwanor]

One thought: if we want to test that the bounding path calculations are correct, we could generate a sorted vector of key hashes $\langle k_1, k_2, ..., k_n \rangle$ (using the TransparentHasher), load them, and then iterate over each key hash $k_i$, mask the last nibble and query the jmt for a proof. What we should obtain as a result is a nonexistence proof for $(k_{i-1}, k_{i+1})$.

[aubrika]

Not adding to V1 currently for scope management but could be elevated if partially done