Upgrade to support 3.11+

[okmich]

Upgrades dynamorm to support python 3.11+.
Given the end-of-life of python 3.10 is 2026-10 (see Python Downloads page), users of this library will be able to continue to use it for higher versions of python runtime.

• Support for python 2 was completed removed
• Support for python 3.11+ and all library dependencies updated as well.
• Source changes to remove dependencies on six library as a result of removing support for python 2.
• Support for schematics 2.1.1 still in place despite the staleness of the project schematic pypi page. The use of this dependency throws warnings at runtime. The support is to ensure users of schematics can port their implementation to marshmallow which is an up-to-date alternative in the future updates.
• No new functionality added

Future work:

• Remove the incompatible schematics library as it has not been updated since 3.9 and the use of this upgrade will show warnings as a result of schematics. See schematic pypi page .

Checklist

• Tests have been written to cover any new or updated functionality
• All tests pass when running tox locally
• The documentation in docs/ has been updated to cover any changes
• The version in setup.py has been bumped to the next version -- follow semver!
• Add an entry to CHANGELOG.rst has been added

@NerdWalletOSS/dynamorm