[FEATURE] [RPC] Implement RPC Request/Response Types

[hulxv]

Description

Design and implement type-safe request and response structures for the RPC framework.

Motivation

Provide a clean API for handling JSON-RPC 2.0 requests and responses with proper error handling.

Proposed Solution

pub struct Request {
    method: String,
    params: serde_json::Value,
    id: Option<RequestId>,
}

impl Request {
    pub fn json<T: DeserializeOwned>(&self) -> Result<T>;
    pub fn param<T>(&self, key: &str) -> Result<T>;
}

Tasks

• Design Request/Response types
• Implement JSON-RPC 2.0 compliance
• Add proper error types
• Support batch requests
• Add validation
• Write unit tests
• Document with examples

Expected

• JSON-RPC 2.0 compliant
• Type-safe parameter extraction
• Proper error handling
• Batch request support

Dependencies:

• Depends on [FEATURE] [RPC] Create mill-rpc Framework Foundation #38