Fail fast on 4xx responses in retry_with_exponential_backoff

[CodexVeritas]

Summary

retry_with_exponential_backoff retried every requests.exceptions.RequestException, including the HTTPError that raise_for_status_with_additional_info raises for deterministic client errors. Every decorated MetaculusClient method retried 4xx responses (e.g. a 400 from an invalid forecast, or a 403 from a restricted endpoint) 3 times, with up to 75s between attempts, before raising the same error.

Changes

• raise_for_status_with_additional_info passes response= to the HTTPError it raises, so the status code travels with the exception. The error message is unchanged.
• retry_with_exponential_backoff re-raises right away when the error is an HTTPError with a 4xx response other than 429, and logs a warning saying why.
• Still retried: timeouts, connection errors, 429, 5xx, and any HTTPError with no response attached (as before).

Tests

Added to code_tests/unit_tests/test_helpers/test_retry_decorator.py (no network or env vars needed):

• A 400 that goes through raise_for_status_with_additional_info is raised after one call, and the response, status code and body text stay on the error.
• 429, 503, HTTPError without a response, Timeout and ConnectionError are each retried max_retries times.

TZ=UTC poetry run pytest code_tests/unit_tests: 994 passed, 141 skipped.

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