feat: add HTTP QUERY method support (RFC 10008)

- Add MethodQuery constant to touka.go
- Add QUERY() convenience method to Engine and RouterGroup
- Add examples/query/main.go demonstrating usage
- All existing tests pass

examples/query/main.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/infinite-iroha/touka"
+)
+
+func main() {
+	r := touka.New()
+
+	// 注册QUERY路由
+	// QUERY方法是RFC 10008定义的新HTTP方法
+	// 它是安全且幂等的，可以携带请求体，适用于复杂查询场景
+	r.QUERY("/search", func(c *touka.Context) {
+		// 获取请求体
+		body, err := c.GetReqBodyFull()
+		if err != nil {
+			c.JSON(http.StatusBadRequest, touka.H{
+				"error": "Failed to read request body",
+			})
+			return
+		}
+
+		// 返回查询结果
+		c.JSON(http.StatusOK, touka.H{
+			"method":      c.Request.Method,
+			"query_body":  string(body),
+			"description": "This is a QUERY request (RFC 10008)",
+		})
+	})
+
+	// 注册路由组
+	api := r.Group("/api").(*touka.RouterGroup)
+	{
+		// 在路由组中使用QUERY
+		api.QUERY("/data", func(c *touka.Context) {
+			body, _ := c.GetReqBodyFull()
+			c.JSON(http.StatusOK, touka.H{
+				"endpoint": "/api/data",
+				"payload":  string(body),
+			})
+		})
+	}
+
+	fmt.Println("Server starting on :8080")
+	fmt.Println("Try: curl -X QUERY http://localhost:8080/search -d '{\"query\": \"test\"}'")
+
+	if err := r.Run(touka.WithAddr(":8080")); err != nil {
+		fmt.Printf("Server error: %v\n", err)
+	}
+}