fix(vscode): should wait for initial scan

[fi3ework]

Summary

fixes a race where the VS Code extension finished its initial test-file scan after the test suite reconfigured rstest.testFileGlobPattern. previously the constructor kicked off scanAllTestFiles without awaiting it, so late completions could repopulate foo.test.ts even when only *.spec.* patterns were allowed.

Related Links

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull Request Overview

This PR fixes a race condition in the VS Code extension where the initial test file scan could complete after test pattern configuration changes, potentially repopulating test files that should be excluded by updated glob patterns.

• Extracts the async scanAllTestFiles operation from the constructor into a separate initialize() method
• Updates the activate() function to await the initialization before returning the extension instance

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