#13 Use safe temporary files in preprocessors and minifiers

[iray-tno]

Summary

• Replace fixed C++ preprocessor/minifier temp filenames with unique NamedTemporaryFile paths.
• Replace fixed Rust rustfmt temp filename with a unique NamedTemporaryFile path.
• Keep cleanup exception-safe with finally blocks.
• Add regression coverage that legacy temp filenames are not created, including formatter-failure cleanup.

Tests

• uv run pytest tests/test_cpp_preprocessor.py tests/test_error_messages.py::TestErrorMessages::test_cpp_formatter_failure_is_reported tests/test_rust_integration.py::TestRustPreprocessorBasic::test_single_file_no_modules -q
• uv run pytest -q

Closes #13.