fix(precompute): keep active panes open

[zzylol]

Before

The wall-clock fallback aged panes from their creation time. A long-running raw or sketch ingest with a fixed event timestamp could therefore force-close a pane while it was still receiving input; subsequent samples were treated as late and dropped. ASAPQuery fixed this in ProjectASAP/ASAPQuery#536, but the fix was missing after the backend split.

After

• Age panes from the most recent raw-sample or prebuilt-sketch touch.
• Preserve idle/trailing-window closure after window_size + grace.
• Cover both active_panes and sketch_panes with deterministic fake-clock regressions.
• Keep the current backend engine and migrate the upstream semantic fix instead of restoring the historical engine.

Verification

• cargo fmt -p data_plane -- --check
• cargo test -p data_plane precompute_engine::worker::tests::wall_clock_fallback -- --nocapture (4 passed)
• cargo test -p data_plane precompute_engine:: (259 passed)

Upstream source: ProjectASAP/ASAPQuery@9a018cb (fix(precompute): keep wall-clock fallback from force-closing panes still under active ingest).