send_tx bug: RequestValidation error

[jaswinder6991]

Problem:
When running the send_tx method, I see the below error:

response: Err(
    ServerError(
        RequestValidationError(
            ParseError {
                error_message: "Unable to parse send request: too many params passed",
            },
        ),
    ),
)

Steps to reproduce:
Run the send_tx example using cargo run --example send_tx

[jaswinder6991]

After doing some digging, I found out that the params method in send_tx is actually creating an array during serialising the parameters.
See here and below:

fn params(&self) -> Result<serde_json::Value, io::Error> {
        Ok(json!([
            common::serialize_signed_transaction(&self.signed_transaction)?,
            self.wait_until
        ]))
    }

Which is a problem for the RpcServer, see here and below:

impl RpcRequest for RpcSendTransactionRequest {
    fn parse(value: Value) -> Result<Self, RpcParseError> {
        let tx_request = Params::new(value)
            .try_singleton(|value| {
                Ok(RpcSendTransactionRequest {
                    signed_transaction: decode_signed_transaction(value)?,
                    // will be ignored in `broadcast_tx_async`, `broadcast_tx_commit`
                    wait_until: Default::default(),
                })
            })
            .try_pair(|_: String, _: String| {
                // Here, we restrict serde parsing object from the array
                // `wait_until` is a new feature supported only in object
                Err(RpcParseError(
                    "Unable to parse send request: too many params passed".to_string(),
                ))
            })
            .unwrap_or_parse()?;
        Ok(tx_request)
    }
}

As you can see arrays are rejected and the error I see is actually thrown here.

I could locally fix this with below changes to the params function in send_tx method in rpc client:

fn params(&self) -> Result<serde_json::Value, io::Error> {
        Ok(json!({
            "signed_tx_base64": common::serialize_signed_transaction(&self.signed_transaction)?,
            "wait_until": self.wait_until
    }))
    } 

Here is a PR for the fix - #142