fix: avoid double call to Strategy.execute() to find out if a feature is enabled

[ClementDelgrange]

Description

This commit https://github.com/Unleash/unleash-client-python/commit/0e7b894851c5a9bec69e9926fcc07a87250fb958 introduced a new method: Feature._get_evaluation_result(context) -> EvaluationResult. This method is used for instance to determine whether a feature is enabled or not. If there are strategies associated to the feature, this method makes a call to strategy.execute(context) and another to enabled_strategy.get_result(context) that itself calls self.execute(context). In the end, Strategy.execute() is called two times which is an issue in the case of a GradualRolloutRandom because a new random integer is compared each time to the rollout percentage.

Steps to follow to highlight the issue:

• create a feature with a gradual rollout and a random stickiness (e.g. https://app.unleash-hosted.com/demo/projects/test-random-stickiness/features/f-random-stickiness)
• set the rollout percentage to 50%
• execute the following script:

  
  from UnleashClient import UnleashClient

api_token = "..." client = UnleashClient( url="https://app.unleash-hosted.com/demo/api/", app_name="my_python_app", custom_headers={"Authorization": api_token} ) client.initialize_client()

total_enabled = sum(client.is_enabled("f-random-stickiness") for i in range(1000))

print(total_enabled) # 228

The change in this pull request proposes to remove the double call to `Strategy.execute()`.

## Type of change

Please delete options that are not relevant.

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
- [ ] This change requires a documentation update

# How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

- [x] Unit tests
- [ ] Spec Tests
- [x] Integration tests / Manual Tests  (manual test with the above snippet)

# Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream modules

[coveralls]

coverage: 96.898% (+0.006%) from 96.892% when pulling 8b9c274f60749cdd4b38bcffb5cf04404eeff913 on ClementDelgrange:main into 0cc36b0ccf20857b9681058d0bb44c5f7847a0bd on Unleash:main.

[ClementDelgrange]

Hello @kwasniew @sighphyre , I saw you were active recently on other pull requests. Is there any chance you could take a look at this one? Please let me know if you need more information or if you'd like me to open an issue to discuss the problem I'm facing.

[kwasniew]

Hey @ClementDelgrange we'll try to handle this PR soon.