Pin JS model integ test to 4.* version

[mollyheamazon]

Summary

Add model_version field to ModelBuilder to allow pinning the JumpStart model version. Previously ModelBuilder hard-coded model_version="*" in its JumpStart resolution path, making it impossible to recover when a JumpStart default points to a broken image (as with meta-textgeneration-llama-2-7b v5.0.0, whose default container fails to start).

Changes

• src/sagemaker/serve/builder/model_builder.py: add model_version: Optional[str] = None field + docstring entry.
• src/sagemaker/serve/builder/jumpstart_builder.py: thread self.model_version into _is_jumpstart_model_id() and _create_pre_trained_js_model(), defaulting to "*".
• tests/unit/sagemaker/serve/builder/test_js_builder.py: 4 unit tests covering default + override at both callsites.
• tests/integ/sagemaker/serve/test_serve_model_builder_inference_component_happy.py: pin fixture to model_version="4.*" to unblock the integ test

Backward compatibility

model_version defaults to None → resolves to "*" at both callsites → identical behavior for all existing callers.

Related

Tracking ticket: link (JumpStart team investigating v5.0.0 CannotStartContainerError).

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