Support Task methods `result()`, `exception()`, and `cancelled()`

CPython's tasks are subclasses of `PyFuture`. This means they have `result`, `exception` methods. They also have a `cancelled` method.

As a user of the asyncio library I want the circuitpython library to support these so I can inspect tasaks more easily from outside `asyncio` - eg, without having to muck around with CircuitPython asyncio task internals like `state` or `data`.

This would require some changes to the core loop for setting these values, but shouldn't be a huge difficulty otherwise? It should be negligible for memory usage / library footprint / etc, unless I'm misunderstanding how the library operates today.

Start by locating the Task implementation and the core loop that manages task state and data. Trace how completion, exceptions, and cancellation are recorded; done means tasks expose result(), exception(), and cancelled() with behavior consistent with the requested asyncio usage, backed by the relevant tests.

Written by the indexing model from the issue text.