(WIP) Implement hash expiration functions

[j00bar]

Fixes #321

Implements the Redis functions for expiration of hash keys.

[j00bar]

I've not actually tested the functionality of the code or set up a proper test environment for it - was in the middle of that when the work day ended yesterday, so safety not guaranteed.

[cunla]

The GitHub workflow should run against different versions of python/redis/redis-py.
But before, please run flake8 and black locally (it should pick up the configuration from pyproject.toml)

[cunla]

Hi, I made a few changes to your branch - and now the github workflow is going to test it against redis 7.4 as well.

[cunla]

Hi,

I updated the code. Some things to notice:

• I removed the timedelta/float tests since they are parsed to int in redis-py. Basically, fakeredis implements redis standards which can be found in the documentation (eg, https://redis.io/docs/latest/commands/hexpire/)
• Notice I implemented _hexpire and _get_expireat as broad implementations and most commands are using them.
• I updated Hash not to inherit from dict since it caused a few issues.

Next steps:

• More tests are required, particularly for "bad cases" (multiple flags, key doesn't exist, etc.)
• Tests for other commands.

[j00bar]

Holy crap. You knocked this out. Thank you so much for the fit and finish and getting it done! Deeply grateful.

[cunla]

Thank you for contributing.
I will release it with a few other things this weekend.