Rust: More path resolution improvements

[hvitved]

Implements a couple of improvements to path resolution:

• Correct handling of mod foo; imports inside nested modules.
• Restrict sibling mod foo; imports to crate entry files and mod.rs files.

[Copilot]

Pull Request Overview

This PR implements improvements to how Rust resolves module paths, focusing on better handling of nested module imports and restricting sibling module imports. Key changes include:

• Adding a new module file at rust/ql/test/library-tests/path-resolution/my/my4/my5/mod.rs.
• Updating rust/ql/test/library-tests/path-resolution/my.rs to re-export a nested module function.
• Enhancing rust/ql/test/library-tests/path-resolution/main.rs with a new module (m18) and its nested structure to test complex resolution scenarios.

Reviewed Changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated no comments.

File	Description
rust/ql/test/library-tests/path-resolution/my/my4/my5/mod.rs	Introduces a new module function f with a test annotation.
rust/ql/test/library-tests/path-resolution/my.rs	Adds a nested module my4 containing my5 and re-exports its function as nested_f.
rust/ql/test/library-tests/path-resolution/main.rs	Adds module m18 with nested modules to test resolution calls using relative paths.

Files not reviewed (2)

• rust/ql/lib/codeql/rust/internal/PathResolution.qll: Language not supported
• rust/ql/test/library-tests/path-resolution/path-resolution.expected: Language not supported

Comments suppressed due to low confidence (3)

rust/ql/test/library-tests/path-resolution/main.rs:489

• [nitpick] The function name 'f' appears in both m18 and m19, which may lead to ambiguity when using relative paths. Consider renaming one of them to clarify which function is being referenced.

                super::f(); // $ item=I102

rust/ql/test/library-tests/path-resolution/main.rs:490

• [nitpick] Using 'super::super::f()' in the context of similarly named functions might be unclear. A more distinct naming scheme could improve readability of the module resolution.

                super::super::f(); // $ item=I101

rust/ql/test/library-tests/path-resolution/my/my4/my5/mod.rs:3

• [nitpick] The annotation 'I201' in the comment may be unclear to future maintainers. Consider providing additional context or a more descriptive comment to indicate its purpose.

} // I201

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[paldepind]

LGTM!