fix(test): Prevent creation of test_data directory during unit tests

[keli-wen]

Description

This PR addresses an issue #39 where running unit tests would create an unexpected test_data directory. This side effect, caused by automatic directory creation in the global Setting model, has been removed to ensure a cleaner developer experience and prevent unintended file system modifications.

Key Changes

• Removed Global Paths: The data_dir and temp_dir fields, along with their validating directory-creation logic, have been removed from the main Setting model in quantmind/config/settings.py.
• Delegated Storage Config: Responsibility for storage paths is now fully delegated to the storage component (e.g., LocalStorageConfig), which manages its own directory structure.
• Updated Tests: Unit tests in tests/config/test_settings.py have been updated to remove checks for the global paths and now perform their own cleanup of storage-related artifacts, ensuring tests are self-contained.
• Updated Examples: All example configurations and scripts have been updated to reflect the new, cleaner structure.

Implementation Notes

The field_validator that created directories upon Setting initialization was the source of the unwanted side effects. By removing it and the associated fields, the Setting class becomes a pure data container, and components like LocalStorage properly encapsulate their own resource management. This enhances modularity and predictability.

Checklist

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