fix: name SQL summary state columns independently of readout parameters

[zzylol]

Why

After #515, structurally identical summary producers are shared across queries. SQL p50 and p99 over the same table, filter and column were still not shared, and neither were PromQL cross-series quantile(0.5, x) / quantile(0.99, x). The KLL state column was named after the query's output column, and that name contains the quantile. For example, SQL produced approx_percentile_cont(lineitem.l_extendedprice,Float64(0.5)) and PromQL produced quantile_0_5. CSE compares schemas, so the two producers never matched, even though the quantile is only a readout parameter.

What

In construct_summary_agg (crates/asap-aware-mapping/src/replacement.rs), a Quantile state that reads a single column is now named after that input column. The column is resolved against the child schema, so SQL gets l_extendedprice and PromQL gets value. This follows the existing UnivMon rule that a state's identity does not depend on which statistic reads it. Output column names are unchanged, because the readout node still produces them.

Effects:

• SQL p50 and p99 share one KLL.
• PromQL cross-series p50 and p99 share one KLL.
• median(x), approx_median(x) and approx_percentile_cont(x, 0.5) share one state.

TopK is unchanged, because k sizes the heap and so is a build parameter.

Tests

• sql_p50_and_p99_share_one_producer: they share, output columns are unchanged, and a different WHERE or a different column is not shared.
• cross_series_p50_and_p99_share_one_producer: fails without the fix.
• Two existing assertions on the old PromQL cross-series state name now expect value. Their output-column assertions are unchanged.

Validation

On Rust 1.99, all of these pass: cargo fmt --check, clippy with -D warnings, the vendored MetricsQL baseline, and cargo test --workspace.

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