Fix issues with resuming async tasks awaiting a future (backport #1469)

[mergify]

Description

Fixes #1467
Fixes #1405
Fixes #1462

Is this user-facing behavior change?

• The _pending() method in Future has been renamed to pending()
• The user no longer has to do any workarounds with waking up the executor when a coroutine gets stuck awaiting a future that is already finished.

Did you use Generative AI?

Some of the comments and docstrings might be partially written by Github Copilot.

Additional Information

For #1467, I propagate a guard condition from a task to the awaited future and add this guard condition to the wait set in the executor. When a future is completed by an entity not controller by the executor (e.g. a separate thread), the guard condition is triggered and wakes up the executor so it can resume the task.

For #1405, I just had to make sure the task is not yielded from _wait_for_ready_callbacks when it is not ready to be resumed, hence the Task.ready() method.

EDIT: Check this comment

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This is an automatic backport of pull request #1469 done by [Mergify](https://mergify.com).

[ahcorde]

Pulls: #1553
Gist: https://gist.githubusercontent.com/ahcorde/f1bd6edae4889fc909f582f6dc07f572/raw/876fef49b9666df3c8ba6e78c400ceb7f6e403e6/ros2.repos
BUILD args: --packages-above-and-dependencies rclpy
TEST args: --packages-above rclpy
ROS Distro: kilted
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/17674

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[bjsowa]

@ahcorde Are the failing sros2 tests my fault or are these unrelated?