Rust: Add tests for web frameworks as taint sources

[geoffw0]

Add tests for web frameworks as taint sources:

• Poem (which we have simple models for, but only a narrow query test).
• Actix (which we have a proposed model for, but no tests at all).
• Axum (which also appears to be popular).

I think these are valuable libraries to model and improve our models for. Alternatively, we might develop a robust heuristic model that covers all three (and potentially others) in one go.

@coadaflorin the tests in mod actix_test below are relevant for #19461 . We could move forward by merging this PR, then merging main into your PR, then reviewing and accepting any difference in test results, then finally merging your PR.

[Copilot]

Pull Request Overview

This PR adds dataflow tests for Rust web frameworks (Poem, Actix, Axum) as taint sources, updates test dependencies, and extends the expected taint source outputs.

• Introduce web_frameworks.rs with handler functions for Poem, Actix, and Axum to verify taint flows.
• Update options.yml to include the new framework dependencies.
• Extend TaintSources.expected with expected taint-source entries for Poem (but currently missing Actix and Axum).

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
rust/ql/test/library-tests/dataflow/sources/web_frameworks.rs	Add handler-based taint-source tests for Poem, Actix, and Axum
rust/ql/test/library-tests/dataflow/sources/options.yml	Add poem, serde, actix-web, axum, and serde_json to deps
rust/ql/test/library-tests/dataflow/sources/TaintSources.expected	Extend expected results with Poem entries (Actix/Axum entries missing)