[RFC] Uniform task spawning (trait version)

[williampMSFT]

This is an option for uniform spawning of tasks. It attempts to make it more difficult to incorrectly use tasks by doing the following three things:

1. Restructure tasks such that only one long-running task is required, and that task does a 'select!' over all the tasks that were previously required. This makes it impossible for users to only launch some of the tasks they need, or to launch them in an order that doesn't work
2. Make each service's init() function return a Result<&'hw Self, ServiceRunner> rather than just a &'hw Self. The user is required to call .run() on the ServiceRunner for the service to function, which they will typically do from a task that they've spawned on their executor. This makes it difficult (but not impossible) for a user to miss spawning the task, because to do that, they have to ignore the ServiceRunner that was returned at init() time, which requires them to explicitly ignore it by binding it to a name with a leading _.
3. Create a spawn_service!() macro that does all the boilerplate of declaring storage and spawning tasks on Embassy for a given service. This doesn't work on Tokio, but Tokio is mostly intended for test usage, where it's generally desirable to select!() over the spawn token and some 'test arm' because that lets the lifetime of the service not be 'static, which is probably what you want for tests.

This variant adds a trait bound to RunnableService that requires an init() function with exactly two arguments. This approach has the upside of catching things that won't work with the spawn_service!() macro at service compile time rather than spawn_service!() instantiation time, but comes at the cost of a bit more ceremony - each service has to declare an 'init params' struct, and instantiation of services requires the RunnableService trait to be in scope.

[Copilot]

Pull request overview

Introduces a new embedded_services::service module that standardizes service initialization and “must-run” task driving via a RunnableService trait, a ServiceRunner handle, and an Embassy-focused spawn_service!() macro. This PR migrates time-alarm-service and espi-service away from per-service task modules to this uniform runner pattern, and updates tests/examples accordingly.

Changes:

• Add RunnableService<'hw>, ServiceRunner, impl_runner_creation_token!(), and spawn_service!() to embedded-service.
• Migrate time-alarm-service to the new init/runner model (remove task module; add ServiceInitParams; implement RunnableService).
• Migrate espi-service to the new runner model (remove task module; add ServiceInitParams; implement RunnableService), and update an Embassy example + Tokio tests to drive via runner.run().

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
time-alarm-service/tests/tad_test.rs	Updates tests to use RunnableService::init() returning (service, runner) and drive via runner.run() in tokio::select!.
time-alarm-service/src/task.rs	Removes the dedicated task wrapper in favor of the new ServiceRunner pattern.
time-alarm-service/src/lib.rs	Adds ServiceInitParams, implements RunnableService, and moves the run-loop into RunnableService::run.
examples/rt685s-evk/src/bin/time_alarm.rs	Switches to embedded_services::spawn_service!() to initialize+spawn the time-alarm service on Embassy.
espi-service/src/task.rs	Removes the dedicated task wrapper in favor of the new ServiceRunner pattern.
espi-service/src/lib.rs	Drops pub mod task export now that the task wrapper is removed.
espi-service/src/espi_service.rs	Adds ServiceInitParams and implements RunnableService (init returns (service, runner), run drives the loop).
embedded-service/src/service.rs	New module defining RunnableService, ServiceRunner, token macro, and spawn_service!() macro.
embedded-service/src/lib.rs	Exposes the new service module.

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 3 comments.

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