Allow selectively running specific queues

[reneklacan]

Summary

• add a repeatable RuntimeBuilder::only_queue::<Q>() allowlist
• run coordinators and cron scheduling only for selected queues
• reject selected queues that were not registered
• document the API and cover default, static, and dynamic queue behavior

Verification

• cargo fmt --all -- --check
• cargo clippy --all-features --workspace (passes with one pre-existing removed-lint warning)
• cargo test -p oxana runtime::tests
• cargo test -p oxana --test integration --no-run
• cargo check --all-features --workspace

The Redis-backed integration test was compiled but not executed locally because REDIS_URL is not configured in this environment.

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Note

Low Risk
Opt-in runtime filtering with unchanged default behavior; misconfiguration is caught at startup when a selected queue is not registered.

Overview
Adds RuntimeBuilder::only_queue::<Q>(), repeatable, so one worker process can register every queue and worker but only run coordinators (and related cron scheduling) for an allowlisted subset. With no only_queue calls, behavior is unchanged: all registered queues run.

RuntimeSettings stores a queue_allowlist; empty means “all queues.” runs_queue gates queue coordinators in the launcher; runs_static_queue skips cron loops whose target queue key is not selected. Selecting a dynamic queue is documented to include all discovered subqueues.

run() fails fast with ConfigError if any selected queue was never registered. Registration and catalog() still list every queue; only execution is filtered.

README documents the API; unit tests cover allowlist defaults, catalog unchanged, dynamic selection, and unregistered selection; an integration test asserts jobs on a non-selected queue stay enqueued.

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