perf(proxy): optimize hot request paths

- Cache route handlers, simplify NoRoute path normalization, and reduce matcher/header allocations

- Honor configured transport pool limits in auto mode and add hotpath regression benchmarks/tests

proxy/reqheader.go

@@ -60,6 +60,17 @@ func copyHeader(dst, src http.Header) {
 	}
 }
 
+func copyHeaderFiltered(dst, src http.Header, denylist map[string]struct{}) {
+	for k, vv := range src {
+		if _, denied := denylist[k]; denied {
+			continue
+		}
+		for _, v := range vv {
+			dst.Add(k, v)
+		}
+	}
+}
+
 func setRequestHeaders(c *touka.Context, req *http.Request, cfg *config.Config, matcher string) {
 	if matcher == "raw" && cfg.Httpc.UseCustomRawHeaders {
 		// 使用预定义Header
@@ -67,14 +78,8 @@ func setRequestHeaders(c *touka.Context, req *http.Request, cfg *config.Config,
 			req.Header.Set(key, value)
 		}
 	} else if matcher == "clone" {
-		copyHeader(req.Header, c.Request.Header)
-		for key := range cloneHeadersToRemove {
-			req.Header.Del(key)
-		}
+		copyHeaderFiltered(req.Header, c.Request.Header, cloneHeadersToRemove)
 	} else {
-		copyHeader(req.Header, c.Request.Header)
-		for key := range reqHeadersToRemove {
-			req.Header.Del(key)
-		}
+		copyHeaderFiltered(req.Header, c.Request.Header, reqHeadersToRemove)
 	}
 }