Rust: Path resolution for extern crates

[hvitved]

I noticed that we were not able to resolve the String struct. This happens because it is reexported using an extern crate definition. This PR adds path resolution support for extern crates, and as the test output witnesses we are now able to resolve String.

DCA shows a whopping 4 percentage point increase in resolved calls (up 54 % from 50 %).

[Copilot]

Pull Request Overview

This PR adds support for resolving items reexported via extern crate, updates core resolution logic, and adjusts test expectations accordingly

• Introduces externCrateEdge and ExternCrateItemNode in PathResolution.qll to handle extern crate imports
• Extends library path-resolution tests (main.rs, my.rs) to validate resolving String and other items through extern crate aliases
• Updates numerous expected outputs and diagnostics (including SummaryStatsReduced.expected) to reflect new path resolutions

Reviewed Changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated no comments.

File	Description
rust/ql/lib/codeql/rust/internal/PathResolution.qll	Added externCrateEdge, ExternCrateItemNode, and stub overrides
rust/ql/test/library-tests/path-resolution/main.rs	Added extern crate self as zelf and updated use to test aliasing
rust/ql/test/library-tests/path-resolution/my.rs	Extended test to assert String resolution via extern crate
rust/ql/test/diagnostics/SummaryStatsReduced.expected	Incremented path resolution inconsistency count

Comments suppressed due to low confidence (3)

rust/ql/lib/codeql/rust/internal/PathResolution.qll:382

• [nitpick] The ExternCrateItemNode.getNamespace override returns none, preventing extern crate aliases from providing a namespace; consider returning an appropriate namespace or documenting why none() is correct.

override Namespace getNamespace() { none() }

rust/ql/lib/codeql/rust/internal/PathResolution.qll:388

• [nitpick] The ExternCrateItemNode.hasCanonicalPath override returns none, which may unintentionally disable canonical path mappings for extern crates; ensure this behavior is intended or implement proper canonical path logic.

override predicate hasCanonicalPath(Crate c) { none() }

rust/ql/lib/codeql/rust/internal/PathResolution.qll:390

• [nitpick] The ExternCrateItemNode.getCanonicalPath override returns none, which may prevent resolution of canonical paths for extern crate items; consider providing a canonical path or clarifying why none() is appropriate.

override string getCanonicalPath(Crate c) { none() }