Add SARIF wire-format regression tests for Artefact renames #397

Summary

Add regression tests that protect the SARIF JSON wire names after the Rust API rename from Artifact to Artefact.

Rationale

The Rust fields now use artefact_location and artefacts, while the SARIF contract must continue to use artifactLocation and artifacts. Round-trip tests can pass when both serialization and deserialization use an incorrect renamed key. Empty collections also do not prove the serialized collection key.

Affected areas

• crates/whitaker_sarif/src/model/location.rs
• crates/whitaker_sarif/src/model/run.rs
• crates/whitaker_sarif/src/builders/run_builder.rs
• SARIF model and builder tests in crates/whitaker_sarif

Required changes

• Serialize a PhysicalLocation with a non-empty artefact_location.
• Assert that JSON contains artifactLocation and does not contain artefact_location.
• Deserialize canonical JSON containing artifactLocation and assert that PhysicalLocation::artefact_location is populated.
• Serialize a Run with a non-empty artefact collection, preferably through RunBuilder::with_artefact.
• Assert that JSON contains artifacts and does not contain artefacts.
• Deserialize canonical JSON containing artifacts.
• Assert that RunBuilder::with_artefact stores the supplied artefact.

Acceptance criteria

• Tests fail if either Serde rename is removed or changed.
• Tests cover serialization and deserialization for populated location and run values.
• Tests directly cover RunBuilder::with_artefact.

Backlinks

• Pull request: Correct en-GB-oxendict spellings in code symbols and prose #363
• Requesting comment: Correct en-GB-oxendict spellings in code symbols and prose #363 (comment)
• Requested by: @leynos