Wallet Connect Session Request Handler

[bh2smith]

This PR, when merged, should minimally meet expectations to close #33. We introduce a method wcRouter that builds relevant byte array payload to for Near MPC contract to sign. It handles all immediately apparent request types (eth_sign, personal_sign, eth_sendTransaction, eth_signTypedData and eth_signTypedData_v4).

Vague Example Usage

From a browser wallet with adapter instance connected to a dapp via Wallet Connect:

Given:

adapter: NearEthAdapter;
request: Web3WalletTypes.SessionRequest;

const { evmMessage, nearPayload } = await adapter.handleSessionRequest(request);

console.log(`Request to sign EVM data ${evmMessage} via MPC Contract` );
console.log(`Payload to sign ${nearPayload}`);

// Execute the near transaction and get the hash
const evmSignature = signatureFromTxHash(nearTxHash);

Note:

1. The evmSignature is still in a form that no front end should have to deal with. More refined signature recovery will be introduced in a follow-up PR.
2. Might also be nice to provide validation of the (evmMessage, nearPayload) pairing construction.

Test Plan

Unit tests are added for each of the supported handler routes.

cc @SurgeCode