test: add Prometheus Remote Write PromQL differential suite

[milindsrivastava1997]

Goal

Port the PromQL-compliance differential-test model into ASAPQuery-backend so the backend is tested as a Prometheus-compatible system end to end.

Outcome

A deterministic suite should:

• start a real Prometheus reference with its Remote Write receiver enabled;
• start the production data_plane --profile asapquery backend with a valid Remote Write PhysicalPlan;
• send the same Snappy/protobuf Remote Write batches to POST /api/v1/write on both systems;
• execute configured instant and range queries against /api/v1/query and /api/v1/query_range;
• compare result type, label set, timestamps, values (with explicit tolerance), and expected errors;
• assert the backend answered locally, so Prometheus fallback cannot mask failures; and
• emit a JSON report and fail CI on differences.

Scope

Reuse/adapt the fixture, Remote Write seeder, comparison/reporting, and Compose lifecycle patterns from ASAPQuery/promql-compliance. Adapt service configuration to the backend's single HTTP listener, its active PhysicalPlan requirement, and its POST /api/v1/precompute/drain finite-input lifecycle.

Start with a small deterministic supported corpus (selectors, aggregation, rate/increase, and supported over-time expressions), then add sparse/staleness and counter-reset cases. Keep existing raw-oracle sketch tests; this suite verifies Prometheus semantics, rather than replacing sketch-accuracy coverage.

Acceptance criteria

• A local one-command invocation provisions/tears down isolated services and writes a report.
• Identical Remote Write payloads are accepted by Prometheus and the backend.
• At least one instant and one range query compare equal without backend fallback.
• A deliberately unsupported/different result fails with an actionable report.
• A small stable suite runs in CI; broader cases may begin as manual/optional.