[FEATURE] Add PPL asynchronous query lifecycle core

[penghuo]

Description

This PR extracts the execution contract and lifecycle core from #7 as the first reviewable implementation slice of opensearch-project#5765. It does not register REST routes or expose the asynchronous API. Existing synchronous PPL behavior remains unchanged.

The execution module exposes one lifecycle-facing contract:

public interface AsyncQueryExecution extends AutoCloseable {
    Optional<QueryResponse> currentResult();
    CompletionStage<Void> completion();
    void close();
}

DefaultAsyncQueryExecution adapts the existing callback execution and publishes only the final result. A successful result is visible through currentResult() before completion() completes normally.

The lifecycle module adds:

• PPLAsyncQueryJob: synchronized state machine for one query.
• PPLAsyncQueryService: registry, timeout race, retention, capacity, task ownership, cancellation, expiration, and cleanup.
• PPLAsyncQueryJobId: opaque owner-routable identifier.
• PPLAsyncQueryUser: retained-job owner identity.
• Async duration and capacity settings.

flowchart LR
    S[PPLAsyncQueryService] --> J[PPLAsyncQueryJob]
    S --> E[AsyncQueryExecution]
    J -->|transition| S
    E -->|completion| S
    S -->|currentResult| E
    S --> T[TaskManager]

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PPLAsyncQueryJob mutates only job-owned state while synchronized. It returns immutable transitions to the service, which performs task cancellation, registry updates, capacity accounting, listener notification, result materialization, and resource cleanup outside the job lock.

PPLQueryRequest changes, async field parsing and defaults, REST actions, owner-node transport routing, response formatting, FGAC integration tests, endpoint documentation, and plugin registration remain in the follow-up public API PR.

Validation

• Contract and final-result ordering tests.
• Job lifecycle, timeout race, lease, capacity, cancellation, cleanup, and concurrency tests.
• Identity and job-ID tests.
• Settings validation tests.
• Spotless checks.

Related Issues

• Part of [FEATURE] Support PPL Async Query opensearch-project/sql#5765.
• Full implementation currently remains available in [FEATURE] Add PPL asynchronous query API #7.

Check List

• New functionality includes testing.
• New public interfaces include Javadoc.
• Commits are signed per the DCO using --signoff.
• Public API documentation will be added in the follow-up PR.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.