Require a context for emulator constructors

[arnobaer]

Require Context as a mandatory constructor argument for all emulator classes.

Update the factory and runtime creation paths to always construct emulators with a Context, and adapt the test suite to the new constructor contract. This unifies emulator initialization and makes context-dependent state available during object construction, e.g.

import random

from comet.emulator import Context, Emulator, message

class MyEmulator(Emulator):
    def __init__(self, context: Context) -> None:
        super().__init__(context)

        options = context.options

        self.humidity_min = options.get("humidity_min", 42.0)  # this was not possible in ctor!
        self.humidity_max = options.get("humidity_max", 43.0)

    @message("HUM\?$")
    def get_humidity(self) -> float:
        return random.uniform(self.humidity_min, self.humidity_max)

This change will permit introducing a service bus in future releases so e.g. scripts then can interact with emulators. via a common TCP socket.