Fix Airbyte deferrable execution timeout deadline evaluation and cleanup

[SameerMesiah97]

Description

This change is a follow-up to PR #67382 and addresses the same execution timeout handling gap that was subsequently fixed for the dbt Cloud provider in PR #67626, but for the Airbyte provider.

It also adopts the deferred timeout buffering approach introduced in PR #67229 for the Kubernetes provider to ensure timeout cleanup logic can execute before Airflow's framework-level deferred timeout handling terminates the task.

The implementation now:

• Uses wall-clock timestamps (time.time()) for serialized deadline calculations instead of monotonic time.
• Enforces execution timeout checks before Airbyte job state evaluation within the trigger.
• Adds a defer timeout buffer to allow timeout events to be processed and Airbyte job cancellation to occur before framework-level deferred timeout handling terminates the task.

Rationale

In deferrable mode, Airbyte job cancellation occurs in execute_complete() when the trigger emits a timeout event. However, Airflow's framework-level deferred timeout handling bypasses execute_complete(), which can leave Airbyte jobs running after task timeout.

Additionally, serialized deadlines must use wall-clock time rather than monotonic time, as they are persisted across defer/resume boundaries. Timeout evaluation must also take precedence over job state evaluation to ensure consistent handling once a deadline has elapsed.

This change keeps timeout handling within the trigger/operator flow and provides sufficient time for Airbyte job cancellation before framework-level task termination occurs.

Tests

Added/modified unit tests verifying that:

• Wall-clock time is used for serialized deadline handling.
• Execution timeout checks take precedence over Airbyte job state evaluation.
• Deferred timeout buffering is applied when execution_timeout is configured.

Backwards Compatibility

This change does not modify public APIs or method signatures.

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