Rust: do not remove Cargo.lock file when running QL tests

[redsun82]

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[Copilot]

Pull Request Overview

This PR stops deleting the Cargo.lock file when preparing QL tests by removing the helper function and its invocation.

• Removed the remove_file_if_exists helper and its call in prepare().
• Dropped the now-unused std::path::Path import.

Comments suppressed due to low confidence (1)

rust/extractor/src/qltest.rs:64

• Consider adding a test to verify that Cargo.lock remains intact after running prepare(), ensuring this change is covered by your test suite.

    set_sources(config)?;