fix: avoid unsafe header buffer reuse

Use safe string copies for pooled header buffers and simplify case-insensitive lookup buffering now that the pseudo stack path was ineffective. This addresses review concerns without changing the routing semantics.

reverseproxy.go

@@ -709,7 +709,7 @@ func (p *reverseProxyHandler) writeLocalOptionsResponse(c *Context) {
 					allowHeader = append(allowHeader, method...)
 				}
 				c.allowHeaderBuf = allowHeader[:0]
-				c.Writer.Header().Set("Allow", BytesToString(allowHeader))
+				c.Writer.Header().Set("Allow", string(allowHeader))
 			}
 		}
 	}