fix(encode): fall back from the literal multiline form when unsafe

Assisted-by: GLM 5.3

docs/API.md

@@ -351,7 +351,10 @@ out, err := interpres.NewEncoder().UseLiteralMultiline(80).Marshal(cfg)
 ```
 
 Single-line strings keep the basic form regardless of the threshold, and a
-threshold of `0` or less disables the option.
+threshold of `0` or less disables the option. A string the literal form cannot
+carry verbatim (an embedded run of three single quotes, a control character
+other than tab, or a carriage return outside a CRLF pair) also keeps the basic
+form, so the output always re-parses to the same value.
 
 ### Cancellation