Provide Peripheral CoroutineScope via scope property

[twyatt]

Peripheral no longer implements CoroutineScope, instead: it is now a scope property.

Per CoroutineScope documentation:

Manual implementation of this interface is not recommended, implementation by delegation should be preferred instead.

CoroutineScope should be declared as a property on entities with a well-defined lifecycle that are responsible for launching child coroutines.

To make the Peripheral API more explicit, it now implements AutoCloseable with close cancelling the Peripheral's coroutine scope (scope property).