[feature-request] Caller witness creation

[stskeeps]

Document how to do a transfer w/ caller witness (smart contract)

[SilentCicero]

@stskeeps this feature is on the way #12 and will become available in @fuel-js/wallet@0.5.2. We can experiment a bit with API's but this is the general format.

// Get the transaction Id for this transfer.
const txTokenId = 1;
const txAddress = '0x1dF62f291b2E969fB0849d99D9Ce41e2F137006e';
const txAmount = utils.parseEther('1');

// Generate the transactionId for this transfer.
const transactionId = await wallet.transfer(txTokenId, txAddress, txAmount, {
    transactionId: true,
});

// Commit the witness, note the contract object can be used by any provider (web3/ethers)
// it just has to contact the `fuel` contract directly and use the `commitWitness(bytes32 transactionId)` ABI.
let commitTx = await wallet.contract.commitWitness(transactionId, {
    gasLimit: 200000,
});

// Here we wait for the transaction to process, but I also increased the number of blocks to let the Fuel aggregator pickup the log.
// We will likely want to add a checking step here (on a loop) to ensure the Fuel sequencer has picked up the witness commitment.
// For now just attempt to do the transfer until it goes through, but wait a few blocks to ensure the sequencer can pick it up, I selected 12 Ethereum blocks here, in ethers.js notation below.
commitTx = await commitTx.wait(12);

// Transfer using Caller witness.
await wallet.transfer(txTokenId, txAddress, txAmount, {
    // Here we provide the necessary event data to build the Caller witness (i.e. `{ blockNumber, address }`)
    caller: commitTx.events[0].args,
});

Anyway, should be in once the PR is reviewed / merged.