executor: Add fallible from_waker getter

[bugadani]

This PR adds a non-panicking way of accessing a task's TimerQueueItem. This allows using integrated timer queues with embassy executors along with some other method for block_on or others.

Split out of #4934

[Copilot]

Pull request overview

This PR adds a fallible variant of the waker-to-task conversion mechanism, enabling non-panicking access to a task's TimerQueueItem. This allows for more flexible integration with embassy executors when using alternative timer queue implementations or block_on methods.

• Adds try_task_from_waker as a fallible alternative to task_from_waker
• Introduces __try_embassy_time_queue_item_from_waker as the public FFI interface
• Updates the panic message to clarify when generic timer queues are involved

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
embassy-executor/src/raw/waker_turbo.rs	Adds try_task_from_waker function for turbowakers mode
embassy-executor/src/raw/waker.rs	Refactors task_from_waker to use new try_task_from_waker helper and updates error message
embassy-executor/src/raw/mod.rs	Adds new FFI function __try_embassy_time_queue_item_from_waker and imports the fallible helper
embassy-executor/CHANGELOG.md	Documents the addition of the new function

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[Copilot]

The changelog entry could be more descriptive. Consider clarifying that this is a fallible variant of __embassy_time_queue_item_from_waker that returns None instead of panicking when the waker is not from Embassy. This would help users understand the purpose of the new function.

Suggested change

	- Added `__try_embassy_time_queue_item_from_waker`
	- Added `__try_embassy_time_queue_item_from_waker`, a fallible variant of `__embassy_time_queue_item_from_waker` that returns `None` instead of panicking when the waker is not from Embassy.