Fix interactive execution of integration tests

[soniapi]

This PR modifies tests/integration_test.rs to allow the integration test to be run interactively.

Problem:
The integration test aggressively mocks stdin using libc::dup2 by default. This causes any manual attempts to run the test and provide terminal inputs to immediately fall through, as the file descriptors have already been pointed to a temporary file containing pre-filled string data ("1\n180000.0\n").

Solution:
Wrapped the standard input mocking block inside an environment variable check (std::env::var("INTERACTIVE").is_err()).

Now, when run with cargo test (like in CI/CD pipelines), INTERACTIVE won't be set, and it will silently mock stdin as it did before.

If a user wishes to run the test manually, they can now execute:
INTERACTIVE=1 cargo test -- --nocapture

And the test will correctly wait for them to type 1 and 180000.0 into the terminal.

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PR created automatically by Jules for task 5341466632526390579 started by @soniapi

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