Configurable Serialization

[northernSage]

Some initial work following #11

• Implement default serializers for each cache type
• Move serializers into separate module
• Extract common serialization logic to BaseSerializer
• add deprecation warning for RedisCache.dump_object and RedisCache.load_object
• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.
• Add new entry to changelog

[northernSage]

In case anyone has any suggestions now would be a good time to let me know while this is still a draft PR, being actively worked on 😉

[northernSage]

Quick update

• If we instantiate FilesystemCache and then overwrite a previously set serializer class attribute (that is what I tried first), management files that are created during instantiation will be serialized with the default serializer and later attempts of deserialization will use the custom serializer which causes UB or just errors out. I'm currently avoiding that by passing the custom serializer to the cache class constructor so it's used from the start even for management files. I'm doing the same thing for all other cache classes to keep it uniform.

• FilesystemCache is a bit different in how it handles timeout values. All cache entries will be stored in their own file along with their timeout value (in the form: <timeout><entry_value>) so the serializer must account for that since every FilesystemCache.get call will first read the timeout to check if the entry has expired and only then will read the actual value of the entry. I still haven't decided if this is something that needs to change in FilesystemCache or if the user should implement their serializer around this as I did with the SillySerializer in the tests.