ttrpc: Add extension framework unit tests and integration tests

The extension framework introduces 10 injection points for wire-format
transforms across the client-server lifecycle.  Without dedicated tests,
regressions in transform ordering (e.g., double-transform on the
streaming_client=false path) or missing injection points would silently
produce incorrect payload bytes.

Add comprehensive test coverage for all 10 injection points:

Unit tests (src/extension.rs, 20 tests):
  - PayloadTransform::transform_inbound / transform_outbound with XOR-0xA5A5
  - transform_inbound_msg / transform_outbound_msg on GenMessage
  - AcceptHook::on_accept with mock TCP socket
  - ConnectHook::on_connect with mock TCP connection
  - ConnectionContext helpers (transform_*_msg delegation)
  - File descriptor passthrough via ConnectionContext
  - Asymmetric transform (distinct inbound/outbound keys)
  - Empty payload edge case

Integration tests (tests/hook_integration_unix.rs, 19 tests):
  - Symmetric client/server hooks with data and transform
  - XOR transform on the wire (end-to-end encryption)
  - Streaming with XOR transform (chunked encrypt/decrypt)
  - streaming_client=false path (server creates faked DATA)
  - streaming_server=false path (rejects DATA, unary only)
  - Multiple concurrent streams on one connection
  - Multiple concurrent connections with transform
  - Unary request timeout
  - Server-initiated stream close
  - Server shutdown during active stream
  - Connect hook called and receives valid raw fd
  - Connect hook rejection fails connection
  - Accept hook called on connection
  - Accept hook rejects connection
  - Connection data propagated to handler
  - No-hook plaintext passthrough (baseline)

Also adds a unit test in src/asynchronous/client.rs verifying that
Client::with_hook fails when the Socket has no raw fd, preventing a
silent downgrade to an untransformed connection.

Signed-off-by: Jiang Liu <gerry@linux.alibaba.com>

Author: jiangliu

src/extension.rs

@@ -101,14 +101,14 @@
 //! The fd is captured in the platform-specific `From` impls (vsock, unix, tcp)
 //! before the socket is type-erased into the inner `Box<dyn AsyncReadWrite>`.
 
+#[cfg(all(unix, feature = "async"))]
+use crate::asynchronous::transport::Socket;
 use std::any::Any;
 use std::collections::HashMap;
 use std::fmt;
-use std::sync::Arc;
 #[cfg(unix)]
 use std::os::unix::io::RawFd;
-#[cfg(all(unix, feature = "async"))]
-use crate::asynchronous::transport::Socket;
+use std::sync::Arc;
 
 /// Type-erased per-connection data store.
 ///
@@ -372,7 +372,6 @@ impl ConnectionContext {
         Ok(None)
     }
 
-
     /// Apply inbound payload transform (if any).
     /// Returns the transformed payload, or the original if no transform is set.
     pub fn transform_inbound(&self, payload: Vec<u8>) -> Result<Vec<u8>, String> {

src/lib.rs

@@ -62,14 +62,13 @@ pub use self::proto::{Code, MessageHeader, Request, Response, Status};
 #[doc(inline)]
 pub use crate::error::{get_status, Error, Result};
 
-#[doc(inline)]
-pub use crate::extension::{
-    HookError, HookOutput, ConnectionContext, ConnectionData, ConnectionDataExt,
-    PayloadTransform,
-};
 #[cfg(unix)]
 #[doc(inline)]
 pub use crate::extension::{AcceptHook, ConnectHook};
+#[doc(inline)]
+pub use crate::extension::{
+    ConnectionContext, ConnectionData, ConnectionDataExt, HookError, HookOutput, PayloadTransform,
+};
 
 cfg_sync! {
     pub mod sync;