Continue making it possible to implement RpcSender (#23561)

* Make nonblocking RpcClient::new_sender pub

As is the blocking RpcClient::new_sender, per #23503.

* Make solana_client::rpc_sender pub

Per #17631 it is supposed to be possible to implement RpcSender in
order to call RpcClient::new_sender. As of now though it is
not possible to name RpcSender in order to implement it.

client/src/lib.rs

@@ -18,7 +18,7 @@ pub mod rpc_deprecated_config;
 pub mod rpc_filter;
 pub mod rpc_request;
 pub mod rpc_response;
-pub(crate) mod rpc_sender;
+pub mod rpc_sender;
 pub mod spinner;
 pub mod thin_client;
 pub mod tpu_client;

client/src/nonblocking/rpc_client.rs

@@ -148,7 +148,7 @@ impl RpcClient {
     /// `RpcSender`. Most applications should use one of the other constructors,
     /// such as [`new`] and [`new_mock`], which create an `RpcClient`
     /// encapsulating an [`HttpSender`] and [`MockSender`] respectively.
-    pub(crate) fn new_sender<T: RpcSender + Send + Sync + 'static>(
+    pub fn new_sender<T: RpcSender + Send + Sync + 'static>(
         sender: T,
         config: RpcClientConfig,
     ) -> Self {