UTBot Python fix bugs

[tamarinvs19]

Description

• Fixed problem with incomparable objects serialisation and code generation (e.g. complex(float('nan')) != complex(float('nan')), but code was generated as if it is comparable)
• Fixed problem with code generation of state assertions (unused variables, incorrect values in comparisons of collections)

How to test

Manual tests

Generate test for python example test cases.

Self-check list

Check off the item if the statement is true. Hint: [x] is a marked item.

Please do not delete the list or its items.

• I've set the proper labels for my PR (at least, for category and component).
• PR title and description are clear and intelligible.
• I've added enough comments to my code, particularly in hard-to-understand areas.
• The functionality I've repaired, changed or added is covered with automated tests.
• Manual tests have been provided optionally.
• The documentation for the functionality I've been working on is up-to-date.