feat(rln): Pmtree implementation

[rymnc]

Currently, we have implemented OptimalMerkleTree(https://github.com/vacp2p/zerokit/blob/1f983bb23226e90b395ff58214f47ae3dca0d634/utils/src/merkle_tree/merkle_tree.rs#L69-L291), and FullMerkleTree(https://github.com/vacp2p/zerokit/blob/1f983bb23226e90b395ff58214f47ae3dca0d634/utils/src/merkle_tree/merkle_tree.rs#L297-L564). We need to do the following to ensure compatibility with the implementation of Pmtree similarly

• [x] Create a trait ZerokitMerkleTree or equivalent, declare the appropriate fns from FullMerkleTree and OptimalMerkleTree
  • [x] https://github.com/vacp2p/zerokit/pull/142
• [x] Update implementations of FullMerkleTree and OptimalMerkleTree to implement the ZerokitMerkleTree trait
  • [x] https://github.com/vacp2p/zerokit/pull/142
• [x] Implement the ZerokitMerkleTree for a struct, PmTree (SledDB, for now), using the pmtree library
• [x] Remove the tests of pmtree here and make tests similar to the other 2 trees, flagged by the pmtree-ft feature
• [x] Update the type of the PoseidonTree to use pmtree if the feature is enabled

This will allow downstream users to use pmtree for atomicity of insertions/deletions.