change to_string return type (#959)

Author: mertcanaltin

include/ada/encoding_type.h

@@ -25,7 +25,7 @@ enum class encoding_type {
 /**
  * Convert a encoding_type to string.
  */
-ada_warn_unused std::string to_string(encoding_type type);
+ada_warn_unused std::string_view to_string(encoding_type type);
 
 }  // namespace ada
 

src/implementation.cpp

@@ -67,7 +67,7 @@ bool can_parse(std::string_view input, const std::string_view* base_input) {
   return result.is_valid;
 }
 
-ada_warn_unused std::string to_string(ada::encoding_type type) {
+ada_warn_unused std::string_view to_string(ada::encoding_type type) {
   switch (type) {
     case ada::encoding_type::UTF8:
       return "UTF-8";