feat(promql): execute binary arithmetic over warm summary readouts

[zzylol]

Audit evidence

ASAPQuery PRs #256, #572, #577, and #644 support native PromQL arithmetic over acceleratable leaves. Current backend QueryPlan has no arithmetic/join node, and physical selection rejects rate(a[1m]) + rate(b[1m]) and rate(a[1m]) / 2. Parent matrix: #501. Upstream plan representation is tracked in ProjectASAP/ASAPPlanner#343.

Required behavior

• Compile Planner arithmetic nodes into QueryPlan operations over warm readouts.
• Implement + - * / % ^, nested expressions, scalar/vector in both orders, and vector/vector default label-set matching.
• Preserve top-k labels when a top-k readout is an operand, as fixed by ASAPQuery Make completed summary windows immutable after durable flush #644.
• Evaluate range requests independently at each step and retain Prometheus NaN/Inf/divide-by-zero behavior.
• Fall back atomically to the exact Prometheus/archive path when any arm is unsupported or unavailable.

Acceptance tests

Add the PR-derived arithmetic cases to process differential E2E for instant and range endpoints and assert warm provenance only when every arm is warm.