fix: validate eth_sendTransaction response is a tx hash not a signature

[ygd58]

Problem

When using the baseAccount wagmi connector, eth_sendTransaction sometimes returns a 65-byte ECDSA signature instead of a standard 32-byte transaction hash. This causes waitForTransactionReceipt() to fail with:

InvalidParamsRpcError: invalid argument 0: hex string has length 130, want 64 for common.Hash

Root Cause

In handleResponse(), eth_sendTransaction fell through to the default case with no validation.

Fix

Added validation in handleResponse() that checks the response is a valid 32-byte tx hash (66 hex chars). If the popup returns a signature instead, a clear error is thrown immediately.

Testing

74/74 tests passed

Closes #251

[cb-heimdall]

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[ygd58]

@fan-zhang-sv @spencerstock Could you please review this PR? It adds validation for eth_sendTransaction response. Thanks!