fix: streamline route matcher backtracking

Avoid rebuilding skipped-node state during wildcard fallback so the matcher no longer loops on the same static branch and stops allocating on the hot path. Add focused route benchmarks and regression coverage to keep the optimized path stable.

engine.go

@@ -739,12 +739,13 @@ func (engine *Engine) handleRequest(c *Context) {
 				c.Redirect(http.StatusMovedPermanently, redirectPath) // 301 永久重定向
 				return
 			}
-			// 尝试不区分大小写的查找
-			// 直接在 rootNode 上调用 findCaseInsensitivePath 方法
-			ciPath, found := rootNode.findCaseInsensitivePath(requestPath, engine.RedirectTrailingSlash)
-			if found && engine.RedirectFixedPath {
-				c.Redirect(http.StatusMovedPermanently, BytesToString(ciPath)) // 301 永久重定向到修正后的路径
-				return
+			if engine.RedirectFixedPath {
+				// 仅在启用固定路径重定向时执行大小写修复查找, 避免无意义的二次树遍历.
+				ciPath, found := rootNode.findCaseInsensitivePath(requestPath, engine.RedirectTrailingSlash)
+				if found {
+					c.Redirect(http.StatusMovedPermanently, BytesToString(ciPath)) // 301 永久重定向到修正后的路径
+					return
+				}
 			}
 		}
 	}