Fluent version mark, v241 settings API tests, removing unnecessary initialize method

[raph-luc]

Obsolete - superseded by #238

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Old text:

WIP - testing:

Closes #114

First steps addressing #178

Changes:

• Adding fluent_version marker for tests, e.g. pytest --fluent-version=24.1
• Adding self_hosted marker for tests, to specify tests that would have issues running on GitHub runners due to resource limitations. pytest --self-hosted runs will only run the self_hosted tests. If --self-hosted is not specified, then the tests marked with self_hosted will not be executed
• Set up CI to run self-hosted tests separately and in parallel to the non-self-hosted runs, speeding up CI
• Changed tests to make use of the GitHub-hosted runners whenever possible, instead of the self-hosted runners, to speed up CI runs
• Added an alternative version to the test_parametric_workflow test, called test_parametric_workflow_settings_api, that uses settings API and removes all direct tui calls
• Added ParametricStudy.reset_study_registry() and ParametricStudyRegistry.clear_registry() methods to deal with issues that were occurring due to pre-existing studies in the current Python interpreter's _shared_parametric_study_registry from previous tests

Update: due to #121, where parametric project save_as calls fail on Windows and GitHub runners, test_parametric_workflow_settings_api was set to run only on self-hosted Linux runners.