Rust: Add a couple of test cases for data flow through conversions

[geoffw0]

Add a couple of test cases for data flow through conversions.

I was interested in the as case, which we do in fact get flow through so no code changes were necessary.

[Copilot]

Pull Request Overview

This PR adds test cases in Rust for verifying data flow through type conversions without requiring changes to core library code.

• Added function "conversions" with various conversion methods using the as, into, and i64::from conversions.
• Updated the main function to invoke the new conversions test.

Files not reviewed (2)

• rust/ql/test/library-tests/dataflow/local/DataFlowStep.expected: Language not supported
• rust/ql/test/library-tests/dataflow/local/inline-flow.expected: Language not supported

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[paldepind]

LGTM.

I assume that once we can write models directly for traits we'll want to write taint steps for From and Into.

Btw, I actually created the dataflow/modeled directory, thinking it should hold tests that are about things being modeled. But I never really made that intention clear to anyone. If you think it's nice to have such a division, we could do that going forward.

[geoffw0]

I assume that once we can write models directly for traits we'll want to write taint steps for From and Into.

Very much yes.

Btw, I actually created the dataflow/modeled directory, thinking it should hold tests that are about things being modeled.

That's great, in practice we'll get coverage from query tests and some other data flow tests as well.