docs: fix performance result analysis examples

[git-jxj]

The performance result-analysis examples use an outdated database representation: request is now JSON text, and decoded OpenAI responses are dictionaries. The current examples fail while attempting to unpickle the request, then fail again when JSON-decoding the response dictionary.

Update both language guides and the bundled analysis script to leave the request text intact and decode only response_messages. Preserve the server response ID when available, with the stored request ID as a fallback for empty or text responses.

Validation:

• Executed all three examples against SQLite databases written by create_result_table / insert_benchmark_data: dictionary, empty, and text responses (0/9 before, 9/9 after).
• 32 related performance tests and the CI-lite smoke test passed.
• make lint, make lint-imports, and git diff --check passed.