feat(sdk): keystore full example

[Mechanix97]

Motivation

New example using the new keystore feature.

Description

This PR adds an example that:

1. Downloads contract deps and compile contract.
2. Creates a new keystore named "RexTest" in the "ContractKeystores" directory.
3. Loads the keystore with the password.
4. Funds the keystore account.
5. Deploys the signer recovery example contract with the keystore account.
6. Prepares the calldata to call the example contract.
   i. Prepares a message.
   ii. Signs the hash of the message with the keystore private key.
   iii. ABI-encodes the parameters.
7. Prepares and send the transaction for calling the example contract.
8. Gets the log emitted by the contract call execution.
9. Compares it with the expected one.

How to test

1. Run a local L1 node (this is optional as this could be tested in a testnet).
2. Run the following command from the root of the repo. The private key must have funds in L1, and the RPC URL defaults to http://localhost:8545:

   cargo run --release --package rex-sdk --example keystore -- --private-key <PRIVATE_KEY> --rpc-url <RPC_URL>

[ilitteri]

Update the PR description and make it step by step:

1. Download contract deps and compile example contract.
2. Create a new keystore named "LambdaClass" in the "ContractKeystores" directory.
3. Load the keystore.
4. Fund the keystore account.
5. Deploy the signer recovery example contract with the keystore account.
6. Prepare the calldata to call the example contract
   1. Prepare a message.
   2. Sign the hash of the message with the keystore private key.
   3. ABI-encode the parameters.
7. Prepare and send the transaction for calling the example contract.
8. Get the log emitted by the contract call execution.
9. Compare it with the expected one.

Do the same for the comments in the code (add 1., 2., etc, consistently with the PRs description).

Also add to the PR description a step by step of how to run this (we should consider adding the rich account private key as an argument, or either the path to a funded keystore).

The requested changes were addressed.