Use a dataclass or NamedTuple for DispatchingActor._scheduled_events items

[llucax]

What's needed?

We need to make the code more naturally readable, as expressions like:

                _logger.debug(
                    "Executing scheduled event: %s", self._scheduled_events[0][1]
                )
                await self._execute_scheduled_event(heappop(self._scheduled_events)[1])
...
            _logger.debug("Next event scheduled at %s", self._scheduled_events[0][0])

are not super readable.

Proposed solution

Instead of tuple[datetime, Dispatch], use something like:

from typing import NamedTuple

class ScheduledDispatchEvent(NamedTuple):
    event_time: datetime
    dispatch: Dispatch

So such expressions can become at least:

                _logger.debug(
                    "Executing scheduled event for dispatch: %s", self._scheduled_events[0].dispatch
                )
                await self._execute_scheduled_event(heappop(self._scheduled_events).dispatch)
...
            _logger.debug("Next event scheduled at %s", self._scheduled_events[0].event_time)