hello Example in Rust

This example demonstrates how to use Rust's powerful features in a NuttX environment, including:

• JSON Serialization/Deserialization: Using the popular serde and serde_json crates to work with JSON data
• Async Runtime: Demonstrates basic usage of the tokio async runtime
• C Interoperability: Shows how to expose Rust functions to be called from C code

Key Features

1. JSON Handling
   • Defines a Person struct with Serialize and Deserialize traits
   • Serializes Rust structs to JSON strings
   • Deserializes JSON strings into Rust structs
   • Demonstrates pretty-printing JSON
2. Async Runtime
   • Initializes a single-threaded tokio runtime
   • Runs a simple async task that prints a message
3. C Interop
   • Exports hello_rust_cargo_main function with #[no_mangle] for C calling
   • Uses extern "C" to define the C ABI

The example shows how Rust's modern features can be used in embedded systems while maintaining compatibility with C-based systems.

This example serves as a foundation for building more complex Rust applications in NuttX that need to handle JSON data and async operations.