test(e2e): answer #509's PromQL examples like the Planner executor

For Examples 1, 3a, 3b, 4a and 4b: plan the workload, start the data_plane
binary against a Prometheus holding generated samples, Remote Write the
same samples, and require every planned query to be answered by the plan
with the Planner executor's result for the workload planned without
ingestion-time state. Exact families must match exactly; Example 3a/4a's
five-year KLL windows exceed k and KLL compaction is randomized, so they
must agree within twice the 0.005 rank target.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: zzylol

README.md

@@ -61,6 +61,14 @@ cargo run -p data_plane -- --plan plan.json --prometheus-url http://localhost:90
 `--capabilities caps.json` replaces the default capabilities, which are the
 Planner executor's capabilities without state kept across query evaluations.
 
+## Examples
+
+`examples/` holds #509's PromQL example workloads (1, 3a, 3b, 4a, 4b) as
+Planner `PlanningWorkload`s. `data_plane/tests/e2e_examples.rs` plans each
+one, runs the `data_plane` binary against a Prometheus holding generated
+samples, Remote Writes the same samples, and checks every planned query
+against the Planner executor running the workload entirely at query time.
+
 ## Development
 
 ```sh