Mimas: more flexible/exensible handling of scenario

[rjgildea]

Use an entry points mechanism to allow enable a more flexible and extensible approach to handling scenarios in mimas.

The simplest mechanism is to register one (or more) functions that take a scenario and return a list of MimasRecipeInvocations or MimasISPyBJobInvocations:

def handle_scenarios(scenario: MimasScenario) -> List[Invocation]:
    return [
        MimasRecipeInvocation(...),
        MimasISPyBJobInvocation(...),
        ...
    ]

This function will handle every scenario passed to the mimas service. Alternatively, a more modular approach can be used, using the @match_specification decorator to filter scenarios that match a given specification before passing them to the function:

from dlstbx.mimas.specification import BeamlineSpecification, DCClassSpecification

is_i99 = BeamlineSpecification("i99")
is_rotation = DCClassSpecification(MimasDCClass.ROTATION)

@match_specification(is_i99 & is_rotation)
def handle_i99_rotation(scenario: MimasScenario) -> List[Invocation]:
    return [
        MimasRecipeInvocation(...),
        MimasISPyBJobInvocation(...),
        ...
    ]

Various commonly used specifications are provided, such as BeamlineSpecification, DCClassSpecification, DetectorClassSpecification, EventSpecification andVisitSpecification. More complex custom specifications may be built by inheriting from ScenarioSpecification. Specifications can be combined using bitwise operators (&, |, ~).

Once this is merged, I would suggest moving the non-DLS-specific components to the python-zocalo repository (see also DiamondLightSource/python-zocalo#129).

[Anthchirp]

This is pretty cool. Love it.