bindings: python: tests: clean up imports and exports

bindings: python: tests: clean up imports and exports

Remove unused imports and sort the remainder following isort rules.

Update the submodules to use `__all__` to advertise available imports.

Remove an unnecessary blank line in the VersionString class to abide by
the ruff formatter's rules (compatible with black's formatting).

Signed-off-by: Vincent Fazio <vfazio@xes-inc.com>
Link: https://lore.kernel.org/r/20241114145116.2123714-17-vfazio@xes-inc.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>