feat(ray-jobs): support runtime environment extensions

[jiangxt2]

Description

This PR adds two explicit, workload-neutral runtime-environment extension inputs to the public Alpha submit_ray_job() helper and the shared build_runtime_env() builder. These inputs are trusted deployment configuration and must not come from broker task payloads. They allow callers to append execution-driver modules after the Tributo Core package and supply an explicit pip package list without scanning the submitting host or discovering provider installations.

The default runtime environment remains unchanged. extra_py_modules preserves caller order after the Core package, while runtime_pip_packages creates Ray's pip field only when non-empty and fails fast when an algorithm artifact owns dependency distribution. Submission identity, reserved identity environment variables, request-digest metadata, ambiguous reconciliation, resource arguments, RayJobSubmission, and BROKER_API_VERSION remain unchanged.

The Broker boundary ADR documents that this is a generic Ray Jobs deployment mechanism rather than a Broker API capability. No Redis or provider dependency, protocol, consume loop, or operation mapping is added to Core.

Related issues

None.

Additional information

• uv run --locked --no-sync python scripts/pr-precheck.py passed after rebasing onto master@bc40056, including format, lint, mypy, dependency and API checks, Python 3.12/3.13 CI parity, changed tests, DCO validation, and documentation gates.
• The changed tests cover default compatibility, extension ordering, explicit pip forwarding, algorithm-artifact ownership conflicts, host-environment isolation, log redaction, Ray submission identity, request-digest metadata, and resource forwarding.
• Docker-based Provider integration tests are outside this Core-only PR because broker transport and Provider healthy paths remain owned by the Provider repository.
• This PR does not change package dependencies or the package version.