json2code: optimize string handling using std::string_view

Replace seastar::sstring with std::string_view for enum string literals
in generated C++ service code. Since these strings are only used for
comparison with HTTP query parameters and don't require modification,
std::string_view provides a more lightweight alternative without the
overhead of string allocation and copying.

This change improves both runtime performance and memory efficiency
of the generated service code.

Signed-off-by: Kefu Chai <[email protected]>

Closes #2657

scripts/seastar-json2code.py

@@ -273,7 +273,7 @@ def indent_body(s, level):
     name_list = ',\n'.join(f'"{enum}"' for enum in enums)
     parse_func = Template('''\
     $type_name str2$type_name(const sstring& str) {
-        static const sstring arr[] = {
+        static const std::string_view arr[] = {
             $name_list
         };
         int i;