add Phase 4 retry attributes

[evaikene]

Changes the standard JobU attribute registry to add retry multiplier and jitter policy values while preserving compatibility with Phase 3 snapshots.

[Copilot]

Pull request overview

This PR updates JobU’s standard attribute registry to introduce Phase 4 retry tuning attributes (retry.jitter and retry.multiplier) and adds/updates tests to ensure older Phase 3 persisted snapshots decode with sensible Phase 4 defaults while keeping partial documents partial.

Changes:

• Extend StandardAttributeRegistry with two new numeric retry attributes, including defaults and validation rules.
• Add/adjust persistence and repository tests to confirm Phase 3-era stored documents missing the new fields are upgraded on materialized decode.
• Add public JSON round-trip coverage for the new retry number attributes.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/jobu-run-attempt-repository-test.cpp	Adds a repository-level regression test ensuring legacy run snapshots load with Phase 4 retry defaults applied.
test/domain-storage-test.cpp	Updates attribute document tests to verify Phase 3 materialized documents are upgraded while partial documents remain partial.
test/attribute-materialization-test.cpp	Expands standard attribute definition/validation tests and adds JSON round-trip coverage for retry.jitter and retry.multiplier.
src/jobu/attribute_registry.hpp	Updates documentation wording and increases the fixed definition array size to include new attributes.
src/jobu/attribute_registry.cpp	Adds the new attribute definitions, defaults, and validation logic for the new numeric fields.

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