feat: add 7 built-in middleware components inspired by Hono.js

New Middleware:
- CORS: Cross-Origin Resource Sharing with full configuration support
- Cookie Helper: Cookie management with signed cookie support (HMAC-SHA256)
- JWT: JSON Web Token authentication (HS256/384/512)
- Bearer Auth: Simple Bearer token authentication
- Compression: Gzip and deflate response compression
- Rate Limiting: Request rate limiting with customizable stores
- Validator: Schema-based request validation

Features:
- Context store for middleware data sharing (get/set/get_client_ip)
- Middleware export module with utility functions
- Comprehensive property-based tests for all middleware
- Example file demonstrating all middleware usage

Files Added:
- cors.v, cookie.v, jwt.v, bearer_auth.v, compress.v, rate_limit.v, validator.v
- middleware.v (unified exports)
- examples/middleware_demo.v
- tests/test_*.v (9 new test files)

Documentation:
- Updated README.md with detailed middleware usage guide
- Added Schema Builder API documentation

cors.v

@@ -0,0 +1,135 @@
+module hono
+
+import net.http
+
+// CorsOrigin 类型 - 支持多种来源配置方式
+// 可以是字符串（单域名或 "*"）、字符串数组（多域名）或回调函数
+pub type CorsOrigin = string | []string | fn (string, Context) string
+
+// CorsOptions 结构体 - CORS 配置选项
+pub struct CorsOptions {
+pub:
+	origin         CorsOrigin = '*'  // 允许的来源，默认允许所有
+	allow_methods  []string   = ['GET', 'HEAD', 'PUT', 'POST', 'DELETE', 'PATCH']
+	allow_headers  []string   = []   // 允许的请求头
+	expose_headers []string   = []   // 暴露的响应头
+	max_age        int             // 预检请求缓存时间（秒），默认 0
+	credentials    bool            // 是否允许凭证，默认 false
+}
+
+// cors - CORS 中间件工厂函数
+// 返回一个 ContextMiddleware，用于处理跨域请求
+pub fn cors(options ...CorsOptions) ContextMiddleware {
+	opts := if options.len > 0 { options[0] } else { CorsOptions{} }
+	
+	return fn [opts] (mut c Context, next fn (mut Context) http.Response) http.Response {
+		// 获取请求的 Origin 头
+		origin := c.req.header.get_custom('Origin') or { '' }
+		
+		// 如果没有 Origin 头，直接继续处理
+		if origin.len == 0 {
+			return next(mut c)
+		}
+		
+		// 计算允许的 Origin
+		allowed_origin := get_allowed_origin(origin, opts.origin, c)
+		
+		// 如果 Origin 不被允许，直接继续处理（不设置 CORS 头）
+		if allowed_origin.len == 0 {
+			return next(mut c)
+		}
+		
+		// 设置 Access-Control-Allow-Origin
+		c.headers['Access-Control-Allow-Origin'] = allowed_origin
+		
+		// 设置 Access-Control-Allow-Credentials
+		if opts.credentials {
+			c.headers['Access-Control-Allow-Credentials'] = 'true'
+		}
+		
+		// 设置 Access-Control-Expose-Headers
+		if opts.expose_headers.len > 0 {
+			c.headers['Access-Control-Expose-Headers'] = opts.expose_headers.join(', ')
+		}
+		
+		// 检查是否为预检请求 (OPTIONS)
+		if c.req.method == http.Method.options {
+			return handle_preflight(mut c, opts)
+		}
+		
+		// 非预检请求，继续处理
+		return next(mut c)
+	}
+}
+
+// get_allowed_origin - 根据配置计算允许的 Origin
+fn get_allowed_origin(request_origin string, origin_config CorsOrigin, c Context) string {
+	match origin_config {
+		string {
+			// 单个字符串配置
+			if origin_config == '*' {
+				// 通配符，允许所有来源
+				return '*'
+			}
+			// 特定域名，检查是否匹配
+			if origin_config == request_origin {
+				return request_origin
+			}
+			return ''
+		}
+		[]string {
+			// 多域名配置，检查请求来源是否在列表中
+			for allowed in origin_config {
+				if allowed == '*' {
+					return '*'
+				}
+				if allowed == request_origin {
+					return request_origin
+				}
+			}
+			return ''
+		}
+		fn (string, Context) string {
+			// 回调函数配置
+			return origin_config(request_origin, c)
+		}
+	}
+}
+
+// handle_preflight - 处理 OPTIONS 预检请求
+fn handle_preflight(mut c Context, opts CorsOptions) http.Response {
+	// 设置 Access-Control-Allow-Methods
+	if opts.allow_methods.len > 0 {
+		c.headers['Access-Control-Allow-Methods'] = opts.allow_methods.join(', ')
+	}
+	
+	// 设置 Access-Control-Allow-Headers
+	if opts.allow_headers.len > 0 {
+		c.headers['Access-Control-Allow-Headers'] = opts.allow_headers.join(', ')
+	} else {
+		// 如果没有配置，尝试使用请求中的 Access-Control-Request-Headers
+		if request_headers := c.req.header.get_custom('Access-Control-Request-Headers') {
+			c.headers['Access-Control-Allow-Headers'] = request_headers
+		}
+	}
+	
+	// 设置 Access-Control-Max-Age
+	if opts.max_age > 0 {
+		c.headers['Access-Control-Max-Age'] = opts.max_age.str()
+	}
+	
+	// 返回 204 No Content
+	c.status(204)
+	
+	mut headers := http.new_header()
+	headers.add_custom('Connection', 'keep-alive') or {}
+	for key, value in c.headers {
+		headers.add_custom(key, value) or { continue }
+	}
+	
+	return http.Response{
+		status_code: c.status_code
+		header: headers
+		body: ''
+	}
+}