fix: always apply evaluator identity keywords and allow explicit domain_id

[jam-jee]

Issue

Evaluator.create() inconsistently applies HubContentSearchKeywords, so some evaluators are silently invisible in SageMaker Studio despite registering successfully in the hub (confirmable via describe-hub-content). Studio filters hub content by keywords such as @subtype:aws/evaluator and @evaluatortype:<type>; when they are missing, the asset exists but never renders in the UI, and no error is raised.

Internal ref: P467494019.

Root cause

In Evaluator.create() the identity keywords were gated behind method is not None:

if method is not None:
    tags = [
        (TAG_KEY_METHOD, method.value),
        ("@subtype", ...), ("@evaluatortype", ...), ("@contenttype", ...),
    ]
else:
    tags = []

method is only resolved for RewardFunction. For RewardPrompt, method stays None, so tags was empty and the only keyword ever attached was @domain (and only inside Studio). The identity keywords describe what the asset is and should never depend on whether a method was resolved.

Changes

• Always attach the identity keywords (@subtype / @evaluatortype / @contenttype) in Evaluator.create(), regardless of evaluator type. Only method remains conditional (reward prompts have no method).
• Add an optional domain_id parameter to Evaluator.create() and DataSet.create(). @domain is already auto-injected inside Studio, but the domain cannot be inferred outside Studio (laptop / CI), leaving assets un-scoped and hidden. Callers can now pass domain_id explicitly; auto-detection is skipped when it is provided. Fully backward compatible (defaults to None).
• Regression tests: identity keywords always present for both RewardFunction and RewardPrompt; explicit domain_id is tagged and auto-detection is not invoked, for both Evaluator and DataSet.

Testing

tests/unit/ai_registry passes (90 tests), including the 3 new regression tests.

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Tests

• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added unit and/or integration tests as appropriate to ensure backward compatibility of the changes