[Bugfix] Prevent segfault when instantiating abstract SearchStrategy

[Dayuxiaoshui]

Add init method to SearchStrategy class to prevent direct instantiation of the abstract class. This raises a TypeError with a helpful error message instead of causing a segmentation fault when SearchStrategy() is called directly or passed to TuneContext.

Also add additional check in TuneContext.init to ensure abstract SearchStrategy instances are not used.

Fixes #18268

[gemini-code-assist]

Summary of Changes

Hello @Dayuxiaoshui, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical bug where direct instantiation of the abstract SearchStrategy class or its usage within TuneContext could lead to a segmentation fault. By implementing explicit type checks and raising informative TypeError exceptions, the change significantly enhances the stability and user-friendliness of the system, guiding users towards correct usage of concrete subclasses or the SearchStrategy.create() factory method.

Highlights

• Prevent Direct Instantiation: Introduced an __init__ method to the SearchStrategy abstract class to explicitly prevent its direct instantiation, raising a TypeError with a descriptive message.
• TuneContext Validation: Added a validation check within TuneContext.__init__ to ensure that an abstract SearchStrategy instance is not inadvertently used, also raising a TypeError.
• New Test Case: Included a new test case, test_search_strategy_abstract_class_instantiation, to confirm that attempts to instantiate the abstract SearchStrategy or pass it to TuneContext correctly result in a TypeError.

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[gemini-code-assist]

Code Review

This pull request effectively prevents a segmentation fault when an abstract SearchStrategy is instantiated by raising a TypeError instead. The changes include adding a check in SearchStrategy's initializer, a redundant but safe check in TuneContext, and a comprehensive test case to verify the fix. My main suggestion is to use __new__ instead of __init__ in SearchStrategy for preventing instantiation, as it is more idiomatic in Python for this purpose. Overall, this is a good fix that improves the robustness of the API.

[tlopex]

LGTM Thanks!