[Rest] Clamp non-finite Retry-After values

[star7js]

Summary

• Add unit test for non-finite Retry-After handling.
• Clamp non-finite Retry-After values (e.g., 1e309 → inf) to max_backoff_seconds.

What Goes Wrong Today

• The library parses Retry-After as a number.
• Extremely large values can become inf, which can break or cause unrealistic sleep behavior.

What The Fix Does

• After parsing, checks whether the value is finite.
• If not finite, clamps it to max_backoff_seconds.
• Uses the safe value for time.sleep.

Why This Is Safe

• The library already clamps large finite values to max_backoff_seconds.
• inf is just “beyond large”; clamping keeps behavior consistent.
• Preserves intended semantics: wait, but not forever.

Tests

• pytest -q tests/test_rest_client.py -k "retry_handler"