Extracts the usable text of a string-typed prompt run: the parsed result when it is a
non-empty string, otherwise the trimmed rawResult (empty string when neither exists).
Lives beside AIPromptRunResult so every caller shares one extraction rule instead
of re-implementing the result-vs-rawResult fallback.
Extracts the usable text of a string-typed prompt run: the parsed
resultwhen it is a non-empty string, otherwise the trimmedrawResult(empty string when neither exists). Lives beside AIPromptRunResult so every caller shares one extraction rule instead of re-implementing theresult-vs-rawResultfallback.