💥 Preserve non-cancellable timed promise waits during cancellation

[Quinn-With-Two-Ns]

What was changed

This change adds the DETACH_NON_CANCELLABLE_PROMISE_GET_TIMER SDK flag and updates timed, non-cancellable Promise.get(timeout, unit) calls to run their timeout timer in a detached cancellation scope. The timer is canceled after the promise completes. Regression and replay tests cover promise completion, timeouts, activity cancellation, child workflow cancellation, and combinations with CANCEL_AWAIT_TIMER_ON_CONDITION. The activity tests use per-test latches for deterministic synchronization.

Why?

Promise.get(timeout, unit) is non-cancellable, but cancellation of its enclosing scope previously canceled its timeout timer. This ended the wait early and incorrectly surfaced a TimeoutException, potentially hiding the actual activity or child workflow cancellation. The new SDK flag preserves replay compatibility for existing workflow histories while allowing new workflows to use the corrected behaviour.

💥 Breaking changes

This change can affect workflow behaviour because timed, non-cancellable Promise.get(timeout, unit) calls will no longer return early with a TimeoutException when their enclosing cancellation scope is canceled. Instead, they will continue waiting until the promise completes, fails, or reaches its actual timeout. Workflows that currently catch the premature TimeoutException and use it to select a control flow path may therefore produce different results. The behaviour is protected by an SDK flag so existing workflow histories retain their original behaviour during replay, while new workflows can adopt the corrected semantics without causing nondeterminism.

Checklist

1. Closes Promise.get(timeout, unit) throws a misleading TimeoutException when the workflow is canceled #3026

2. How was this tested:

3. Any docs updates needed?

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Note

High Risk
Changes core workflow promise/cancellation semantics behind an SDK flag; enabling it alters control flow for workflows that relied on premature timeouts when scopes were canceled.

Overview
Fixes incorrect TimeoutException when a CancellationScope is canceled while a non-cancellable Promise.get(timeout, unit) is waiting: the enclosing cancellation used to cancel the internal await timer and end the wait early.

Introduces SdkFlag.DETACH_NON_CANCELLABLE_PROMISE_GET_TIMER (pending enablement) and, when that flag is present in execution metadata, runs the timed await inside a detached cancellation scope and cancels that scope in a finally after the wait finishes. WorkflowInternal.checkSdkFlag exposes flag lookup for CompletablePromiseImpl. cancellableGet is unchanged.

Adds parameterized integration tests (promise completion, real timeout, activity/child cancellation) plus 12 replay history fixtures covering combinations with CANCEL_AWAIT_TIMER_ON_CONDITION.

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