Add TypeDict object for typehinting for Exception handler callbacks

[Vizonex]

What do these changes do?

These changes are made to better reflect the documentation on Exception Handlers as mentioned in #565
Might need a little help & Guidance with this one :/

Are there changes in behavior for the user?

Typehinting changes for Exception Handler Callbacks mainly meant to assist and add context from the provided documentation

Related issue number

Fixes #565

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes

[Vizonex]

@Dreamsorcerer I'll come back sometime in a couple of hours later today to mark a few mypy things off as ignorable because the default handler expects a something other than a context instead of something else. Here's the error from the workflow if you need a bit of context something to mark these as truthy in the python code might be nessesary...

aiojobs/_job.py:151:46: error: Argument 1 to "call_exception_handler" of
"Scheduler" has incompatible type "dict[str, object]"; expected
"ExceptionHandlerDict"  [arg-type]
                scheduler.call_exception_handler(context)
                                                 ^~~~~~~
aiojobs/_job.py:182:48: error: Argument 1 to "call_exception_handler" of
"Scheduler" has incompatible type "dict[str, object]"; expected
"ExceptionHandlerDict"  [arg-type]
            self._scheduler.call_exception_handler(context)
                                                   ^~~~~~~
aiojobs/_scheduler.py:31:10: error: Missing type parameters for generic type
"Job"  [type-arg]
        job: Job
             ^
aiojobs/_scheduler.py:239:63: error: Argument 1 to "call_exception_handler" of
"AbstractEventLoop" has incompatible type "ExceptionHandlerDict"; expected
"dict[str, Any]"  [arg-type]
                asyncio.get_running_loop().call_exception_handler(context)
                                                                  ^~~~~~~
tests/test_scheduler.py:241:38: error: Argument 1 to "call_exception_handler"
of "Scheduler" has incompatible type "dict[str, str]"; expected
"ExceptionHandlerDict"  [arg-type]
        scheduler.call_exception_handler(d)
                                         ^
Found 5 errors in 3 files (checked 9 source files)

[Dreamsorcerer]

aiojobs/_scheduler.py:239:63 is essentially a bug/limitation in mypy. The others are typing issues in our code that should be fixed.