Event Refactor

[mitsuhiko]

Fixes durable await_event timeout handling across SQL and all SDKs.

• Adds an explicit timed_out return column to absurd.await_event so timeouts are no longer inferred from payload = null.
• Persists event timeouts as timed_out checkpoints, allowing timeout progress to replay durably instead of re-sleeping or repeating earlier work.
• Updates the Python, TypeScript, and Go SDKs to consume the new result shape while preserving compatibility with older two-column await_event implementations.
• Ensures cancellation is checked before replaying a persisted timeout, so cancellation is not masked by a previous timeout.

Previously, timeout detection relied on a legacy sentinel shape: should_suspend = false and payload = null. That made real JSON null event payloads ambiguous and meant timeout progress was not durably checkpointed in the same way as successful event payloads.