feat(sdk): add Swift and Kotlin mobile client foundations with push token proto

Swift SDK: Swift Package wrapping libquicproquo_ffi with QpqClient class
(connect, login, send, receive, disconnect) for iOS 15+ / macOS 13+.

Kotlin SDK: JNI bridge to libquicproquo_ffi with QpqClient class for
Android (aarch64, armv7) and JVM, Gradle build configuration.

Adds RegisterPushToken RPC (method ID 710) to device.proto for
APNs/FCM/WebPush device push token registration.

crates/quicproquo-proto/src/lib.rs

@@ -116,10 +116,11 @@ pub mod method_ids {
     pub const UPLOAD_BLOB: u16 = 600;
     pub const DOWNLOAD_BLOB: u16 = 601;
 
-    // Device (700-702)
+    // Device (700-702, 710)
     pub const REGISTER_DEVICE: u16 = 700;
     pub const LIST_DEVICES: u16 = 701;
     pub const REVOKE_DEVICE: u16 = 702;
+    pub const REGISTER_PUSH_TOKEN: u16 = 710;
 
     // P2P (800-802)
     pub const PUBLISH_ENDPOINT: u16 = 800;