This change updates the project structure to become flattened.
Previously, the simulator, frontend and API each lived into their own
directory.

With this change, all modules of the project live in the top-level
directory of the repository. This should improve discoverability of
modules of the project.

This change removes the StateFlow speed property on the
SimResourceSource, as the overhead of emitting changes to the StateFlow
is too high in a single-thread context. Our new approach is to use
direct callbacks and counters.

This change updates the resource model implementation to cache the
remaining work field, which was being computed multiple times during the
same cycle.

This change adds support for transforming the resource commands emitted
by the resource consumers. The SimResourceForwarder is modified to also
support transforming the resource commands.

This change re-enables support for VM usage metrics by adding an adapter
for SimResourceConsumer instances that can export the consumer speed.

This change adds support for dynamically changing the capacity of
resources and propagating this change to consumers.

This change removes the generic resource constraint (e.g., SimResource)
and replaces it by a simple capacity property. In the future, users
should handle the resource properties on a higher level.

This change simplifies compositions of consumers and providers by not
requiring a translation from resource to capacity.

This change changes the consumer and context interfaces to expose the
provider capacity and remaining work via the context instance as opposed
to only via the callback. This simplifies aggregation of resources.

This change re-designs the SimResourceConsumer interface to support in
the future capacity negotiation. This basically means that the consumer
will be informed directly when not enough capacity is available, instead
of after the deadline specified by the consumer.

This change moves the hypervisor implementations to the
opendc-simulator-resources module and makes them generic to the resource
type that is being used (e.g., CPU, disk or networking).