feat: create mappers functions for file paths

[AlexTheWizardL]

This pull request covers 2 functions:

1. file_id_to_path()
2. file_path_to_id()

This functions will help to easily find id or path in the cached files.

@lasuk Please review the changes and provide feedback or approval for merging.

[lasuk]

I've added two commits:

• bbca34bc with minor modifications to prettify code and fix checks
• e5038436 to improve the logic of pytest fixtures.

@AlexTheWizardL: I've left a TODO in the code. Can you address this (restore files on the CashCtrl server to the initial state before the test startet)? Thanks

# TODO: We should restore original files after the test is complete

[lasuk]

Let's also override below methods in CashedCashCtrlClient. The overridden methods will first call the parent class method and after that invalidate the corresponding cache:

mirror_directory()
upload_file()
update_categories()

[lasuk]

Thanks! Merging.