feat(sdk-android): Kotlin wire protocol matching the Go encoder

Uses org.json (already on Android; org.json:json test dep for JVM
unit tests). Field names and framing mirror internal/agent/protocol.go
so Go-encoded frames decode on the SDK without a shared schema file.

sdk/android/build.gradle.kts

@@ -24,4 +24,5 @@ android {
 
 dependencies {
     testImplementation("junit:junit:4.13.2")
+    testImplementation("org.json:json:20240303")
 }