v0.1.2 of singbox_ffi

Flutter FFI bindings and platform packaging for embedding the sing-box libbox core from Dart. Changelog excerpt: - Add Dart-facing log draining and streaming APIs. - Add native sb_drain_logsand sb_clear_logsABI functions backed by libbox's started-service log subscription. - Add SingboxLogEvent, SingboxService.logs(), drainLogs(), and clearLogs()for UI log panels.