[feature/jmt (4/4]: In memory implementation of Jmt backed by storage traits + tests

[acerone85]

This feature implements a Jmt backed by two in-memory hashmaps (for the tree nodes and value preimages), and an optional value (to keep track of the latest version of the tree). The implementation makes use of the generic implementation of a Jmt over storage traits.

The following tests are provided:

• Check root hash for empty tree
• Check that restoring a tree to a previous state yields the original root hash
• Test that the tree changes when updating the tree
• Test a valid proof of exclusion on the empty tree
• Test a valid proof of inclusion on a non-empty tree
• Test a valid proof of exclusion on a non-empty tree
• Test that a tampered proof of inclusion is non-valid
• Test multiple proofs of inclusion and exclusion on a tree with 1000 leaves

[Short description of the changes.]

Checklist

• Breaking changes are clearly marked as such in the PR description and changelog
• New behavior is reflected in tests
• If performance characteristic of an instruction change, update gas costs as well or make a follow-up PR for that
• The specification matches the implemented behavior (link update PR if changes are needed)

Before requesting review

• I have reviewed the code myself
• I have created follow-up issues caused by this PR and linked them here

After merging, notify other teams

[Add or remove entries as needed]

• Rust SDK
• Sway compiler
• Platform documentation (for out-of-organization contributors, the person merging the PR will do this)
• Someone else?

[netrome]

Nice tests!

[netrome]

Can you divide the tests into "Given", "When" and "Then" sections?