Rust: Don't apply generated models for functions that have a manual model

[paldepind]

Also

• fixes a wrong manual model for as_path which was previously covered up by another wrong generated model 😅
• Promotes a generated model for Pin::new to a manual model. The model is not precise, but not having it caused a bunch of test failures (here for instance) so it's probably best to keep it until we can get those results the precise way.

[Copilot]

Pull request overview

This pull request enhances the Rust dataflow model system to prevent generated models from being applied when manual models exist for the same function. This ensures that manual models, which are typically more precise, take precedence over automatically generated ones.

Key changes:

• Implements logic to filter out generated models when manual models exist for a function
• Fixes an incorrect manual model for PathBuf::as_path
• Promotes a Pin::new model to manual status to preserve test results

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
rust/ql/lib/codeql/rust/dataflow/internal/ModelsAsData.qll	Adds hasManualModel() predicate and updates propagatesFlow() to exclude generated models when manual models exist
rust/ql/lib/codeql/rust/frameworks/stdlib/fs.model.yml	Fixes the as_path model specification from Argument[Self] to Argument[self].Reference
rust/ql/lib/codeql/rust/frameworks/stdlib/core.model.yml	Adds a new manual model for Pin::new to handle implicit dereference cases
rust/ql/test/library-tests/dataflow/models/models.ext.yml	Adds test models for the snd function to verify the fix works correctly
rust/ql/test/library-tests/dataflow/models/main.rs	Adds test case for snd function demonstrating that wrong generated model is ignored
rust/ql/test/library-tests/dataflow/models/models.expected	Updates expected test output to reflect the new behavior
rust/ql/test/library-tests/dataflow/sources/file/InlineFlow.expected	Updates expected output to reflect the corrected as_path model

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[paldepind]

Thanks for the review. Merging as DCA is uneventful.