Substrate Wrapper - Issue serializating extrinsics

[willemolding]

Currently this test is failing with an error:

{
 "jsonrpc": "2.0",
 "error":
 {
  "code": 1002,
  "message": "Verification Error: Runtime error: Execution failed: Error calling api function: Failed to convert parameter `tx` from node to runtime of validate_transaction",
  "data": "RuntimeApi(\"Execution failed: Error calling api function: Failed to convert parameter `tx` from node to runtime of validate_transaction\")"
 },
 "id": 1
}

Most likely this is a but in how the extrinsics and/or signatures are serialized prior to sending to the chain. This needs looking into and ideally some Rust tests added to unit test the serialization logic.