completely rewrite pq_proto (#12085)

libs/pqproto is designed for safekeeper/pageserver with maximum
throughput.

proxy only needs it for handshakes/authentication where throughput is
not a concern but memory efficiency is. For this reason, we switch to
using read_exact and only allocating as much memory as we need to.

All reads return a `&'a [u8]` instead of a `Bytes` because accidental
sharing of bytes can cause fragmentation. Returning the reference
enforces all callers only hold onto the bytes they absolutely need. For
example, before this change, `pqproto` was allocating 8KiB for the
initial read `BytesMut`, and proxy was holding the `Bytes` in the
`StartupMessageParams` for the entire connection through to passthrough.

proxy/src/context/mod.rs

@@ -4,7 +4,6 @@ use std::net::IpAddr;
 
 use chrono::Utc;
 use once_cell::sync::OnceCell;
-use pq_proto::StartupMessageParams;
 use smol_str::SmolStr;
 use tokio::sync::mpsc;
 use tracing::field::display;
@@ -20,6 +19,7 @@ use crate::metrics::{
     ConnectOutcome, InvalidEndpointsGroup, LatencyAccumulated, LatencyTimer, Metrics, Protocol,
     Waiting,
 };
+use crate::pqproto::StartupMessageParams;
 use crate::protocol2::{ConnectionInfo, ConnectionInfoExtra};
 use crate::types::{DbName, EndpointId, RoleName};
 

proxy/src/context/parquet.rs

@@ -11,7 +11,6 @@ use parquet::file::metadata::RowGroupMetaDataPtr;
 use parquet::file::properties::{DEFAULT_PAGE_SIZE, WriterProperties, WriterPropertiesPtr};
 use parquet::file::writer::SerializedFileWriter;
 use parquet::record::RecordWriter;
-use pq_proto::StartupMessageParams;
 use remote_storage::{GenericRemoteStorage, RemotePath, RemoteStorageConfig, TimeoutOrCancel};
 use serde::ser::SerializeMap;
 use tokio::sync::mpsc;
@@ -24,6 +23,7 @@ use super::{LOG_CHAN, RequestContextInner};
 use crate::config::remote_storage_from_toml;
 use crate::context::LOG_CHAN_DISCONNECT;
 use crate::ext::TaskExt;
+use crate::pqproto::StartupMessageParams;
 
 #[derive(clap::Args, Clone, Debug)]
 pub struct ParquetUploadArgs {