perf(proxy): reduce nest rewrite allocations

- Dispatch shell link rewriting between streaming and buffered paths based on response size

- Reuse buffers and reduce URL construction allocations in proxy handlers

- Add nest benchmarks and align extractParts compatibility expectations with the current contract

proxy/chunkreq.go

@@ -74,7 +74,7 @@ func ChunkedProxyRequest(ctx context.Context, c *touka.Context, u string, cfg *c
 	// 处理响应体大小限制
 
 	var (
-		bodySize      int
+		bodySize      = -1
 		contentLength string
 		sizelimit     int
 	)
@@ -134,7 +134,7 @@ func ChunkedProxyRequest(ctx context.Context, c *touka.Context, u string, cfg *c
 
 		var reader io.Reader
 
-		reader, _, err = processLinks(bodyReader, c.Request.Host, cfg, c)
+		reader, _, err = processLinks(bodyReader, c.Request.Host, cfg, c, bodySize)
 		c.WriteStream(reader)
 		if err != nil {
 			c.Errorf("%s %s %s %s %s Failed to copy response body: %v", c.ClientIP(), c.Request.Method, u, c.UserAgent(), c.Request.Proto, err)