* hub: tick delay fix

todo and timer callbacks can perform actions that
require a tick callback to be executed right away
without polling.

the current order can cause issues
when using single worker with no prefetch (acks late).

related issue in celery:
https://github.com/celery/celery/issues/7718

* add unit test for hub delay fix

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

* Annotate init files

* Fix fmatch_best annotation

When there is no locking then there is a possibility that multiple threads
manipulate with the same object at the same time.
The issue is manifested as:
```
RuntimeError: Set changed size during iteration
```

See: https://github.com/celery/celery/issues/7162

* enable pre-commit

* use extend-ignore for flake8

* manual flake8 fixes

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update kombu/__init__.py

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

* reset ready before execute callback

* add test to cover hub._ready reset to empty

According to [PEP-479](https://www.python.org/dev/peps/pep-0479/) StopIteration should not be used any more to indicate the termination of a generator.
Starting from Python 3.7 this behaviour is always enforced and a RuntimeError is raised instead.
We now return instead of raising StopIteration.