Fix cross-platform test fixture failures on Windows

[hardikkaurani]

Description

This PR resolves cross-platform test fixture failures on Windows by replacing POSIX-specific shell commands with Python standard library operations.

Problem

In test/test_retriever.py and test/test_regression.py, test setup and teardown fixtures (setup_module, teardown_module, and test_setup_functions) invoked POSIX-specific commands via subprocess.call(['cp', '-r', ...]) and subprocess.call(['rm', '-r', ...]).

On Windows systems where POSIX binaries are not natively available in PATH, this resulted in FileNotFoundError: [WinError 2] The system cannot find the file specified, causing all tests in these modules to fail during fixture initialization.

Proposed Changes

• Replaced subprocess.call(['cp', '-r', ...]) with shutil.copytree() in test/test_retriever.py and test/test_regression.py.
• Replaced subprocess.call(['rm', '-r', ...]) with shutil.rmtree() and os.remove() for directory and file cleanups.
• Pre-cleaned destination paths prior to copying to maintain compatibility with Python 3.7+ without requiring the Python 3.8+ dirs_exist_ok keyword argument.

Verification

• Ran pytest test/test_retriever.py on Windows with Python 3.11.9: fixture setup and teardown executed successfully without FileNotFoundError.
• Ran pytest test/test_regression.py on Windows: fixture setup, teardown, and SQLite/CSV regression tests completed successfully.
• Verified that git diff --check reports no whitespace or formatting regressions.

[Copilot]

🟢 Approval recommended

The changes are test-only and correctly replace POSIX-specific commands with cross-platform Python equivalents, with only a minor cleanup nit noted.

Pull request overview

This PR updates test fixtures to be cross-platform (especially Windows) by removing reliance on POSIX cp/rm shell commands and using Python’s standard library for filesystem setup/cleanup.

Changes:

• Replaced subprocess.call(['cp', '-r', ...]) with shutil.copytree() in test module setup to copy test/raw_data into the expected raw_data location.
• Replaced subprocess.call(['rm', '-r', ...]) with shutil.rmtree() / os.remove() in teardown and related cleanup paths.
• Added pre-cleaning of destination paths to keep compatibility with Python versions that don’t support dirs_exist_ok.

File summaries

File	Description
test/test_retriever.py	Switches fixture setup/teardown and test cleanup from POSIX shell commands to shutil/os operations for Windows compatibility.
test/test_regression.py	Applies the same cross-platform filesystem changes to regression test setup/teardown and SQLite cleanup.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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