feat: add sendDtmf method to send DTMF tones during a call

ios/Classes/LiblinphoneFlutterPlugin.swift

@@ -209,7 +209,21 @@ public class LiblinphoneFlutterPlugin: NSObject, FlutterPlugin {
         case "syncCurrentState" :
             linphoneBridge.syncCurrentState()
             result(true)
+
+        case "sendDtmf":
+            guard let args = call.arguments as? [String: Any],
+                  let tone = args["tone"] as? String else {
+                result(FlutterError(
+                    code: "INVALID_ARGUMENTS",
+                    message: "Missing required arguments",
+                    details: nil
+                ))
+                return
+            }
             
+            let success = linphoneBridge.sendDtmf(tone: tone)
+            result(success)
+
         default:
             result(FlutterMethodNotImplemented)
         }

ios/Classes/LinphoneBridge.swift

@@ -241,7 +241,7 @@ class LinphoneBridge {
         guard let params = currentCall?.currentParams else {
             return .unknown
         }
-        
+
         if params.videoEnabled {
             return .video
         } else {
@@ -249,6 +249,25 @@ class LinphoneBridge {
         }
     }
 
+    func sendDtmf(tone: String) -> Bool {
+        guard let call = currentCall else {
+            return false
+        }
+        
+        guard !tone.isEmpty else {
+            return false
+        }
+        
+        let dtmfChar = tone.first!
+        do {
+            try call.sendDtmf(dtmf: CChar(dtmfChar.asciiValue!))
+            return true
+        } catch {
+            print("Error sending DTMF: \(error)")
+            return false
+        }
+    }
+
     func syncCurrentState() {
         onRegistrationStateChanged(registrationState.rawValue)
         onCallStateChanged(callState.rawValue)