[flake8] Enable flake8-bugbear extension

[stinodego]

Relates to #4044

Changes:

• Enabled the flake8-bugbear extension. (flake8 extensions are enabled simply by being installed in the same environment as flake8)
• Fixed the resulting linting errors. Some of the more interesting ones:
  • B009: There is some inconsistency in type hints when it comes to DataTypes vs instantiated DataTypes. We should look into this at some point. For now, replaced the getattr with the proper usage and ignored the resulting mypy error.
  • B006: The deepcopy function definition was a fun rabbithole... apparently the optional memo is required, but this is very poorly documented. We do not use it, so we can just set it to None. (for reference, the pandas DataFrame deepcopy does the same)