[client] Move ICE and relay workers into the worker package

Relocate WorkerICE (renamed worker.ICE) and WorkerRelay plus ConnPriority
into client/internal/peer/worker. To break the peer<->worker cycle the
workers no longer take *Conn or ConnConfig: callbacks are passed as plain
functions (Conn's unexported methods as method values), and each worker
receives only the fields it needs (key, ICE config, isController) plus a
small services struct. Context is passed to OnNewOffer instead of stored.

Move the worker connection-status helper the other way, out of the worker
package into peer as worker_status.go (WorkerStatus / AtomicWorkerStatus),
since only Conn uses it.

client/internal/peer/worker_status.go

@@ -0,0 +1,55 @@
+package peer
+
+import (
+	"sync/atomic"
+
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	WorkerStatusDisconnected WorkerStatus = iota
+	WorkerStatusConnected
+)
+
+type WorkerStatus int32
+
+func (s WorkerStatus) String() string {
+	switch s {
+	case WorkerStatusDisconnected:
+		return "Disconnected"
+	case WorkerStatusConnected:
+		return "Connected"
+	default:
+		log.Errorf("unknown status: %d", s)
+		return "unknown"
+	}
+}
+
+// AtomicWorkerStatus is a thread-safe wrapper for worker status
+type AtomicWorkerStatus struct {
+	status atomic.Int32
+}
+
+func NewAtomicStatus() *AtomicWorkerStatus {
+	acs := &AtomicWorkerStatus{}
+	acs.SetDisconnected()
+	return acs
+}
+
+// Get returns the current connection status
+func (acs *AtomicWorkerStatus) Get() WorkerStatus {
+	return WorkerStatus(acs.status.Load())
+}
+
+func (acs *AtomicWorkerStatus) SetConnected() {
+	acs.status.Store(int32(WorkerStatusConnected))
+}
+
+func (acs *AtomicWorkerStatus) SetDisconnected() {
+	acs.status.Store(int32(WorkerStatusDisconnected))
+}
+
+// String returns the string representation of the current status
+func (acs *AtomicWorkerStatus) String() string {
+	return acs.Get().String()
+}