refactor: refine byte pools usage and fix memory leak in rules

internal/route/rules/template.go

@@ -8,6 +8,7 @@ import (
 
 type templateOrStr interface {
 	Execute(w io.Writer, data any) error
+	Len() int
 }
 
 type strTemplate string
@@ -23,6 +24,10 @@ func (t strTemplate) Execute(w io.Writer, _ any) error {
 	return nil
 }
 
+func (t strTemplate) Len() int {
+	return len(t)
+}
+
 type keyValueTemplate = Tuple[string, templateOrStr]
 
 func executeRequestTemplateString(tmpl templateOrStr, r *http.Request) (string, error) {