Consider using `TypedDict` for 2nd `ExceptionHandler` parameter

[sh-at-cs]

The ExceptionHandler type is currently defined as taking a dict[str, Any] as its 2nd parameter:

aiojobs/aiojobs/_scheduler.py

Line 29 in 70fe9e5

ExceptionHandler = Callable[["Scheduler", Dict[str, Any]], None]

But the docs explain that the set of keys of this dictionary is actually static:

aiojobs/docs/api.rst

Lines 161 to 168 in 70fe9e5

	*context* is a :class:`dict` with the following keys:
	* *message*: error message, :class:`str`
	* *job*: failed job, :class:`Job` instance
	* *exception*: caught exception, :exc:`Exception` instance
	* *source_traceback*: a traceback at the moment of job creation
	(present only for debug event loops, see also
	:envvar:`PYTHONASYNCIODEBUG`).

So it would be better for type-safety (and things that come with it like IDE completion) if this used a TypedDict instead of a generic dict[str, Any].

[Dreamsorcerer]

Sound right. That'd be an excellent contribution and would also verify that the code is actually behaving as per the documentation.