feat: align test suits

[AlexTheWizardL]

This PR covers changes that align test suits to a common standard.

1. Removed docstrings from test suits and renamed them instead. Example:

from:

def test_keep_extra_columns() -> None:
    """Test dropping columns not in the required or optional lists."""

to:

def test_drop_extra_columns_with_keep_extra_columns_false():

2. Deleted useless branches of code that are not possible by the system, specifically we can not have entries with the same ID. Example (this code is removed):

   elif len(result) > 1:
           raise ValueError(f"Multiple paths found for account category id: {id}")

3. Removed useless type hints for the fixtures and tests suits. For further details, see the discussions on type annotations for fixtures, the pytest documentation and the Django project.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Flag	Coverage Δ
unittests	93.86% <100.00%> (+0.72%)	:arrow_up:

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Files	Coverage Δ
cashctrl_api/cashed_client.py	94.02% <ø> (+1.83%)	:arrow_up:
cashctrl_api/client.py	92.95% <100.00%> (ø)