[proxy] remove TokioMechanism and HyperMechanism (#12672)

Another go at #12341. LKB-2497

We now only need 1 connect mechanism (and 1 more for testing) which
saves us some code and complexity. We should be able to remove the final
connect mechanism when we create a separate worker task for
pglb->compute connections - either via QUIC streams or via in-memory
channels.

This also now ensures that connect_once always returns a ConnectionError
type - something simple enough we can probably define a serialisation
for in pglb.

* I've abstracted connect_to_compute to always use TcpMechanism and the
ProxyConfig.
* I've abstracted connect_to_compute_and_auth to perform authentication,
managing any retries for stale computes
* I had to introduce a separate `managed` function for taking ownership
of the compute connection into the Client/Connection pair

libs/proxy/tokio-postgres2/src/connect.rs

@@ -7,7 +7,7 @@ use tokio::net::TcpStream;
 use tokio::sync::mpsc;
 
 use crate::client::SocketConfig;
-use crate::config::Host;
+use crate::config::{Host, SslMode};
 use crate::connect_raw::StartupStream;
 use crate::connect_socket::connect_socket;
 use crate::tls::{MakeTlsConnect, TlsConnect};
@@ -45,14 +45,36 @@ where
     T: TlsConnect<TcpStream>,
 {
     let socket = connect_socket(host_addr, host, port, config.connect_timeout).await?;
-    let mut stream = config.tls_and_authenticate(socket, tls).await?;
+    let stream = config.tls_and_authenticate(socket, tls).await?;
+    managed(
+        stream,
+        host_addr,
+        host.clone(),
+        port,
+        config.ssl_mode,
+        config.connect_timeout,
+    )
+    .await
+}
+
+pub async fn managed<TlsStream>(
+    mut stream: StartupStream<TcpStream, TlsStream>,
+    host_addr: Option<IpAddr>,
+    host: Host,
+    port: u16,
+    ssl_mode: SslMode,
+    connect_timeout: Option<std::time::Duration>,
+) -> Result<(Client, Connection<TcpStream, TlsStream>), Error>
+where
+    TlsStream: AsyncRead + AsyncWrite + Unpin,
+{
     let (process_id, secret_key) = wait_until_ready(&mut stream).await?;
 
     let socket_config = SocketConfig {
         host_addr,
-        host: host.clone(),
+        host,
         port,
-        connect_timeout: config.connect_timeout,
+        connect_timeout,
     };
 
     let (client_tx, conn_rx) = mpsc::unbounded_channel();
@@ -61,7 +83,7 @@ where
         client_tx,
         client_rx,
         socket_config,
-        config.ssl_mode,
+        ssl_mode,
         process_id,
         secret_key,
     );

libs/proxy/tokio-postgres2/src/lib.rs

@@ -48,7 +48,7 @@ mod cancel_token;
 mod client;
 mod codec;
 pub mod config;
-mod connect;
+pub mod connect;
 pub mod connect_raw;
 mod connect_socket;
 mod connect_tls;