Forks in python fuzzing and refactoring

[tamarinvs19]

Description

Fuzzing forks

• Used forks in python fuzzing: now we can go back to previous annotation with history having.
• Current strategy: try to go back to the best annotations per 12 attempts.
• Current results (number of executions per second) is not worse then previous version on examples.
• Suitable case: samples/controlflow/conditions.py. Here we can set a big timeout and cover all branches through returning to the previous annotations.

Execution counter

• Added cli argument --execution-counter to save a number of executions. It can be helpful if you need to measure the speed of utbot python
• Added some scripts in samples/testing_utils to collect and show executions information.

Code refactoring

• Small cosmetic changes

How to test

Automated tests

Run run_tests_all.sh and check that all examples have expected coverage

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.

[Markoutte]

LGTM