Add lastSpokeAt property to Swift SDK (#818)

This PR adds the lastSpokeAt property to the Swift SDK to align with
Android and JS implementations.
It represents the last time a participant spoke, allowing consistent
behavior across platforms.

Author: brainwith

.changes/last-spoke-at

@@ -0,0 +1 @@
+patch type="added" "Add lastSpokeAt property to Participant"

Sources/LiveKit/Core/Room+EngineDelegate.swift

@@ -107,13 +107,19 @@ extension Room {
                 if participantSid == localParticipant.sid {
                     localParticipant._state.mutate {
                         $0.audioLevel = speaker.level
+                        if !$0.isSpeaking {
+                            $0.lastSpokeAt = Date()
+                        }
                         $0.isSpeaking = true
                     }
                     activeSpeakers.append(localParticipant)
                 } else {
                     if let participant = state.remoteParticipant(forSid: participantSid) {
                         participant._state.mutate {
                             $0.audioLevel = speaker.level
+                            if !$0.isSpeaking {
+                                $0.lastSpokeAt = Date()
+                            }
                             $0.isSpeaking = true
                         }
                         activeSpeakers.append(participant)

Sources/LiveKit/Core/Room+SignalClientDelegate.swift

@@ -146,6 +146,9 @@ extension Room: SignalClientDelegate {
 
                 participant._state.mutate {
                     $0.audioLevel = speaker.level
+                    if !$0.isSpeaking, speaker.active {
+                        $0.lastSpokeAt = Date()
+                    }
                     $0.isSpeaking = speaker.active
                 }
 

Sources/LiveKit/Participant/Participant.swift

@@ -40,6 +40,9 @@ public class Participant: NSObject, @unchecked Sendable, ObservableObject, Logga
     @objc
     public var isSpeaking: Bool { _state.isSpeaking }
 
+    @objc
+    public var lastSpokeAt: Date? { _state.lastSpokeAt }
+
     @objc
     public var metadata: String? { _state.metadata }
 
@@ -88,6 +91,7 @@ public class Participant: NSObject, @unchecked Sendable, ObservableObject, Logga
         var name: String?
         var audioLevel: Float = 0.0
         var isSpeaking: Bool = false
+        var lastSpokeAt: Date?
         var metadata: String?
         var joinedAt: Date?
         var kind: Kind = .unknown