Revisit functionality and naming of remaining query/readout terms after statistic renames #550

Follow-up from review comments on #549, which renamed SketchQuery → SketchStatistic and PopulationReadout → PopulationStatistic.

The enum renames fixed the type names, but the surrounding vocabulary still uses the old terms:

• query: SummaryExpr::SummaryEstimate still has a query: PostAsapSketchStatistic field, and related code still says query (review comment, crates/asap-aware-mapping/src/replacement.rs). Should this be renamed too?
• readout: maintained-population code still uses readout for locals, fields, and functions after the enum became PopulationStatistic (review comment, crates/asap-aware-mapping/src/maintained_population.rs). Should all of the readout names be renamed?

Proposal

Don't just rename these mechanically. First check what these fields and functions actually do, then pick names that match:

1. For each place that uses query / readout, work out what it does: is it a requested statistic (a description of the result), the act of extracting or estimating from a summary, or an execution step?
2. Rename based on that. Something that only describes the requested statistic should line up with *Statistic. Something that actually performs extraction/estimation may deserve a separate, action-style name (or should stay separate from the statistic type).
3. Keep naming consistent across types, asap-aware-mapping, asap-physical-operators, and the docs.

Relation to #509

This ties into the planner layering in #509 (docs/design_docs/proposals/planner-layering.md). Which names are right depends on which stage/layer owns each concept: the logical description of a requested statistic vs. the physical/execution step that produces it. The renames should follow that staging-and-functionality split, so that each name shows which layer it belongs to.