Clean up temporary download archives

[vansh-nagar]

Fixes #168.

The download path converted its TempPath into a PathBuf before providers ran, which dropped the cleanup guard. Keep that guard alive while removing only the initial placeholder, so providers can recreate the path and the fetched file is removed after success or failure. Plain-file downloads still move the fetched file into place as before.

Regression tests cover successful extraction plus fetch, verification, and extraction failures.

Tests:

• cargo test
• cargo clippy
• cargo fmt -- --check

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