Apache Fory Swift & Dart gRPC integration

Apache Fory's compiler can generate type bindings for seven languages, but neither Swift nor Dart have gRPC service generation support. The generate_services() extension point exists in BaseGenerator and is wired into the CLI, but no language implements it yet. This project adds that support for both: Dart will get a new compiler generator (dart.py) covering messages, enums, and unions alongside gRPC stub generation, while Swift will extend the existing SwiftGenerator with generate_services(). Both will emit typed service interfaces and transport bindings using Fory's serialize/deserialize APIs as the codec, covering all four RPC streaming modes with a zero-copy decode path where possible, without introducing any gRPC dependency into the Fory runtimes. Deliverables include the Dart compiler generator, gRPC stubs with golden tests for both languages, runnable server and client examples, cross-language round-trip tests against a Java server, and compiler documentation for the --grpc flag.