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

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)