[relay] Replace net.Conn with context-aware Conn interface (#5770)

* [relay] Replace net.Conn with context-aware Conn interface for relay transports

Introduce a listener.Conn interface with context-based Read/Write methods,
replacing net.Conn throughout the relay server. This enables proper timeout
propagation (e.g. handshake timeout) without goroutine-based workarounds
and removes unused LocalAddr/SetDeadline methods from WS and QUIC conns.

* [relay] Refactor Peer context management to ensure proper cleanup

Integrate context creation (`context.WithCancel`) directly in `NewPeer` and remove redundant initialization in `Work`. Add `ctxCancel` calls to ensure context is properly canceled during `Close` operations.

relay/server/server.go

@@ -3,7 +3,6 @@ package server
 import (
 	"context"
 	"crypto/tls"
-	"net"
 	"net/url"
 	"sync"
 
@@ -31,7 +30,7 @@ type ListenerConfig struct {
 // In a new HTTP connection, the server will accept the connection and pass it to the Relay server via the Accept method.
 type Server struct {
 	relay       *Relay
-	listeners   []listener.Listener
+	listeners   []Listener
 	listenerMux sync.Mutex
 }
 
@@ -56,7 +55,7 @@ func NewServer(config Config) (*Server, error) {
 	}
 	return &Server{
 		relay:     relay,
-		listeners: make([]listener.Listener, 0, 2),
+		listeners: make([]Listener, 0, 2),
 	}, nil
 }
 
@@ -86,7 +85,7 @@ func (r *Server) Listen(cfg ListenerConfig) error {
 	wg := sync.WaitGroup{}
 	for _, l := range r.listeners {
 		wg.Add(1)
-		go func(listener listener.Listener) {
+		go func(listener Listener) {
 			defer wg.Done()
 			errChan <- listener.Listen(r.relay.Accept)
 		}(l)
@@ -139,6 +138,6 @@ func (r *Server) InstanceURL() url.URL {
 // RelayAccept returns the relay's Accept function for handling incoming connections.
 // This allows external HTTP handlers to route connections to the relay without
 // starting the relay's own listeners.
-func (r *Server) RelayAccept() func(conn net.Conn) {
+func (r *Server) RelayAccept() func(conn listener.Conn) {
 	return r.relay.Accept
 }