Basic preemption policies.

Factory for `preemption-policy`.

Registry for `preemption-policy`.

A resource is a limited quantity of items that are used by entities as they proceed through the system. A resource has a capacity that governs the total quantity of items that may be available. All the items in the resource are homogeneous, meaning that they are indistinguishable. If an entity attempts to seize a resource that does not have any units available it must wait in a queue.
It is often representing real world items that availability is limited (e.g. machine, wrench, ...).

A resource knows its instantenous capacity, its policies,and the element waiting for its availablility in the queue. The properties of a resource are:
* `capacity` (default 1) total number of available resources, note that this number may evolve over time.
* `currently-consuming` (default []) list of events currently consuming this resource, is useful to track them and enabling preemption and failures. The event contains the information on the waiting entity.
* `preemption-policy` (default ::sim-de-rc/no-preemption) is the policy to apply when a resource is consumed and none is available.
* `queue` (default []) list of blocked entities.
* `renewable?` (default true) when true, the disposing is not giving back the values.
* `unblocking-policy` (default ::simde-rc/FIFO) refers to an entity from the `automaton-simulation-de.rc.policies` registry, that registry will allow to pick one element in a queue.

Resource consumption is what is happening when a resource is available and an entity seizing it.

A consumption has two steps, a consume and a free of the resource.
The resource updates a `::sim-de-rc/currently-consuming` list events that are consuming resources

The queue of a resource is containing all event execution which are blocked while waiting for a resource to be available.

Store and update resource consumer informations in the `::sim-rc/resource` key of the state.
Assuming state is associative.

The simple policies to unblock an event in the queue.

Factory to return the `unblocking-policy`.

Registry for `unblocking-policy`.