MILP: Raqe lacks a keyed sketch's key labels (topk-of-sum heap pricing and sharing) #854

Problem

rqe_optimizer::Raqe has no field for the labels a keyed sketch is keyed by. For a top-k-of-sum query, topk(k, sum by (l) (f(m[w]))), the heap holds one key per l value, but the Raqe's grouping is the top-k bucket grouping ([] for a global top-k). This causes two problems:

1. Pricing. require_shapes and the accuracy curves read data_shape[[]], the per-series shape. The heap's key count is bounded by the series count, so sizing errs large, but accuracy curves measured on per-series values may not match summed values. The chosen depth, width and heap size are therefore not grounded in the actual key set.
2. Sharing. Two top-k Raqes on one metric whose heaps need different keys (sum by (job) vs sum by (instance)) look identical to the solver. feat(planner): collapse topk(sum by (l) (sum_over_time)) into one CMS heap #849 makes plan_to_planner_output refuse such a plan (DeploymentLabelsDisagree) instead of writing a wrongly keyed heap, but the solver should never propose it.

Fix direction

Add key labels to sketch-bench's Raqe, as part of its stream/deployment identity, and price keyed sketches from data_shape[key labels]. Then populate the field in build_raqe (asap-planner-rs/src/optimizer/milp.rs) and remove the ponytail: note there.