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

android/src/main/kotlin/xyz/nuark/liblinphone_flutter/LiblinphoneFlutterPlugin.kt

@@ -185,6 +185,17 @@ class LiblinphoneFlutterPlugin : FlutterPlugin, ActivityAware, MethodCallHandler
                 result.success(true)
             }
 
+            "sendDtmf" -> {
+                try {
+                    val tone = call.argument<String>("tone")!!
+                    val res = linphoneBridge.sendDtmf(tone)
+                    result.success(res)
+                } catch (e: Exception) {
+                    Log.e(TAG, "sendDtmf: ${e.message}")
+                    result.error("error", e.message, e)
+                }
+            }
+
             else -> {
                 result.notImplemented()
             }

android/src/main/kotlin/xyz/nuark/liblinphone_flutter/LinphoneBridge.kt

@@ -364,4 +364,18 @@ class LinphoneBridge(
         }
         return CallType.Unknown
     }
+
+    fun sendDtmf(tone: String): Boolean {
+        if (currentCall == null) {
+            return false
+        }
+        
+        if (tone.isEmpty()) {
+            return false
+        }
+        
+        val dtmfChar = tone[0]
+        currentCall?.sendDtmf(dtmfChar)
+        return true
+    }
 }