Initial signer sync

[SupremoUGH]

Goes together with:

• Initial pull method Manta#1046
• Initial signer sync sdk#108

Implements the Initial Synchronization method for the signer. For that, there's a new method that creates a partial Merkle tree from a vector of leaves and a path, extended to forked trees and forests.
On the wallet side, we read the relevant data from the ledger and then use it to update the signer, without any Poseidon hash computation (as opposed to the usual sync method).

Design choice:

• I chose to instantiate the MK from a path instead of a SinglePath MK. Using the second, we could check the roots of coincide, making it more secure, and less trusting on the pulled data. However, I think the data pulled from the Ledger is considered trusted, so no need for additional computations.

On the testing/simulation: Besides the new unit tests for the partial and forked MKs, I ran the simulation, kept the Ledger, and then re-ran it again with new actors which would do the initial sync w.r.t. the new ledger. It all went smoothly, as expected. The code was quite clumsy and it'd take a long time to make it look better (and add nice features like new actors joining the simulation at arbitrary times) so I removed that part, but it's good to know that it worked as expected.

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• Linked to an issue with discussion and accepted design OR have an explanation in the PR that describes this work.
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• Checked that changes and commits conform to the standards outlined in CONTRIBUTING.md.

[Apokalip]

lgmt