fix: cut redirect and allow-path routing overhead

Reuse fixed-path and Allow-header buffers so redirect and OPTIONS handling stop rebuilding temporary data on every request. Cache fallback chains and add regression coverage for redirect, 404, 405, and Allow behavior to keep the faster miss paths stable.

context.go

@@ -73,6 +73,12 @@ type Context struct {
 	// skippedNodes 用于记录跳过的节点信息，以便回溯
 	// 通常在处理嵌套路由时使用
 	SkippedNodes []skippedNode
+
+	// fixedPathBuf 用于复用固定路径重定向时的大小写修正结果缓冲.
+	fixedPathBuf []byte
+
+	allowedMethodsBuf []string
+	allowHeaderBuf    []byte
 }
 
 // --- Context 相关方法实现 ---
@@ -111,6 +117,15 @@ func (c *Context) reset(w http.ResponseWriter, req *http.Request) {
 	} else {
 		c.SkippedNodes = make([]skippedNode, 0, 256)
 	}
+	if cap(c.fixedPathBuf) > 0 {
+		c.fixedPathBuf = c.fixedPathBuf[:0]
+	}
+	if cap(c.allowedMethodsBuf) > 0 {
+		c.allowedMethodsBuf = c.allowedMethodsBuf[:0]
+	}
+	if cap(c.allowHeaderBuf) > 0 {
+		c.allowHeaderBuf = c.allowHeaderBuf[:0]
+	}
 }
 
 // Next 在处理链中执行下一个处理函数