Add quic-client module (#23166)

* Add quic-client module to send transactions via quic, abstracted behind the TpuConnection trait (along with a legacy UDP implementation of TpuConnection) and change thin-client to use TpuConnection

sdk/src/client.rs

@@ -175,6 +175,8 @@ pub trait AsyncClient {
     /// Send a signed transaction, but don't wait to see if the server accepted it.
     fn async_send_transaction(&self, transaction: transaction::Transaction) -> Result<Signature>;
 
+    fn async_send_batch(&self, transactions: Vec<transaction::Transaction>) -> Result<()>;
+
     /// Create a transaction from the given message, and send it to the
     /// server, but don't wait for to see if the server accepted it.
     fn async_send_message<T: Signers>(

sdk/src/quic.rs

@@ -1 +1,5 @@
 pub const QUIC_PORT_OFFSET: u16 = 6;
+// Empirically found max number of concurrent streams
+// that seems to maximize TPS on GCE (higher values don't seem to
+// give significant improvement or seem to impact stability)
+pub const QUIC_MAX_CONCURRENT_STREAMS: usize = 2048;