fix(promql): preserve special quantile parameters for exact execution

[zzylol]

Why

Valid PromQL quantile parameters must reach execution so the engine can return the Prometheus-defined special values.

What

Accept out-of-range, NaN, and infinite phi in standard quantile functions. Keep the bounded parameter contract of the nonstandard histogram_quantiles extension.

How

Preserve phi during lowering instead of rejecting it; retain a separate bounded validator for the extension.

Before this PR

quantile_over_time(1.1, m[5m]) failed during lowering, preventing an exact backend plan.

After this PR

The canonical tree retains phi=1.1 so an executor can return +Inf. Regression coverage also pins the already-supported distinction between rate/irate and series-count semantics.

Evidence

The new parameter regression accepts -0.1, 1.1, NaN, +Inf, and -Inf across quantile, quantile_over_time, and histogram_quantile. Backend execution coverage: ProjectASAP/ASAPQuery-backend#728. Screenshots and performance measurements: not applicable.

Verification

cargo +1.98.0 test -p asap-frontend-promql --test promql_binding_regressions --test promql_lowering --test promql_conformance --test promql_equivalence passed on this branch.

The parameter regression checks valid queries survive lowering; the other regressions prevent rate/irate or row/distinct-count intent collapse.

Architectural decisions

No new execution interface. Validation distinguishes standard PromQL from the existing extension contract.

Limitations and follow-up

This PR preserves parameters; executors remain responsible for special-value results. The backend companion adds float-sample exact execution and differential smoke coverage. It pins f27b16a747e5d7fcd70a5510075c0cd062f0dcea, the same fix applied on its existing 029ff2f dependency so its current interfaces remain available.

Human review — do not complete with an agent

• The MVP boundary is correct.
• New conceptual layers or public interfaces are necessary.
• The before/after description matches the intended product behavior.
• Human reviewer:
• Decision and rationale: