Rust: Handle writes to references and add encoding of reference content

[paldepind]

No description provided.

[Copilot]

PR Overview

This PR adds and updates data flow tests in multiple Rust files to handle cases involving mutable references, updated annotations for reference-based flows in model generator files, and clarifications around reference handling in MyOption methods.

• Introduces new tests for functions that mutate arguments via references.
• Adds or refines data flow summaries in model generator to track references more accurately.
• Updates pointer-related data flow tests to confirm flow through borrowed references.

Changes

File	Description
rust/ql/test/library-tests/dataflow/global/main.rs	Adds functions mutates_argument_1 and mutates_argument_2 to test data flow from source to sink via mutable references.
rust/ql/test/utils-tests/modelgenerator/summaries.rs	Adds reference-based data flow summaries set_int and read_int for improved data flow tracking.
rust/ql/test/utils-tests/modelgenerator/option.rs	Adjusts generated summaries to handle references in MyOption methods, clarifying argument and return flows.
rust/ql/test/library-tests/dataflow/pointers/main.rs	Enhances pointer tests to verify clearing data after flow, ensuring correct data flow through mutable borrows.

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[Copilot]

This comment indicates a missing data flow annotation for the value from source(88). Consider adding the correct annotation or removing the note to reflect the intended test behavior accurately.

Suggested change

	sink(n); // $ MISSING: hasValueFlow=88
	sink(n); // $ hasValueFlow=88

[geoffw0]

Obviously there's more to be done in future, but this looks like a solid step forward.

I'd like to see a DCA run.

[paldepind]

DCA is uneventful as far as I can see.