fix: include sender address in gas estimation for ERC-20 compatibility

[ryanRfox]

Summary

This PR fixes a critical bug where ERC-20 token transfers fail with ERC20: transfer from the zero address during gas estimation. The fix adds proper sender address handling to the estimateGas() method.

Fixes #9

Changes

• Added optional from?: Address parameter to estimateGas() method
• Modified prepareTx() to pass the signer's address to estimateGas() when available
• Added JSDoc documentation explaining when from is required
• Added comprehensive tests for the fix

Problem

When calling eth_estimateGas without a from address, Ethereum nodes default to address(0). This causes any contract that validates msg.sender to fail during gas estimation.

Before (Broken)

async estimateGas(tx: Transaction): Promise<bigint> {
  const estimate = await this.ethClient.estimateGas({
    to: tx.to?.ethAddress(),
    data: tx.data ? eth.hexlify(tx.data) : undefined,
    value: tx.value,
    // Missing: from address
  });
}

After (Fixed)

async estimateGas(tx: Transaction, from?: Address): Promise<bigint> {
  const estimate = await this.ethClient.estimateGas({
    from: from?.ethAddress(),  // Now includes sender address
    to: tx.to?.ethAddress(),
    data: tx.data ? eth.hexlify(tx.data) : undefined,
    value: tx.value,
  });
}

How Other SDKs Handle This

SDK	Implementation
ethers.js v6	Automatically populates from when transaction is connected to a Signer
viem	Requires explicit account parameter for estimateGas

Our fix aligns with ethers.js behavior - automatically including the sender when available while maintaining backward compatibility.

Testing

New Tests Added (6 tests in test/gas-estimation.test.ts)

1. ERC-20 token transfer succeeds with the fix
2. estimateGas with explicit from parameter returns valid estimate
3. estimateGas with from parameter works for contract calls
4. Backward compatibility: estimateGas without from works for native transfers
5. Backward compatibility: estimateGas without from works for contract deployments
6. Contract.execute correctly estimates gas for ERC-20 transfers

Test Results

✓ test/gas-estimation.test.ts (6 tests) 3313ms
✓ test/integration.test.ts (2 tests) 3037ms

Test Files  2 passed
Tests       8 passed

Manual Verification

Successfully transferred SBC/ISB tokens on Radius testnet after applying the fix.

Breaking Changes

None - This fix is fully backward compatible:

• estimateGas(tx) continues to work (from defaults to undefined)
• All existing code paths remain functional
• New from parameter is optional

Checklist

• Code follows project style guidelines
• JSDoc documentation added for new parameter
• All new tests pass
• All existing tests pass
• Manual testing on testnet completed
• No breaking changes introduced