feat(aqe): support executor failure in AdaptiveExecutionGraph

[jja725]

Summary

Implements the unchecked "support executor failure" task from the AQE epic #1359. Brings AdaptiveExecutionGraph to parity with StaticExecutionGraph's executor-loss recovery so re-running stages and rolled-back stages work end-to-end under AQE.

Problem

AdaptiveExecutionGraph::reset_stages_on_lost_executor was structurally a copy of the static-graph version, but it was a no-op in practice for AQE because:

1. AQE's create_resolved_stage initialises stage.inputs to an empty HashMap (intentional — partition locations live in the planner's plan tree under ExchangeExec.shuffle_partitions, not in stage.inputs). The static-graph rollback walk thus found nothing.
2. The AdaptivePlanner's side state (runnable_stage_cache, runnable_stage_output) was never told about lost executors, so a re-running successful stage failed with Can't find active stage to update stage outputs.
3. ExchangeExec / AdaptiveDatafusionExec in the live plan tree retained shuffle_partitions = Some(...) even after their owning stage rolled back, so find_runnable_exchanges would skip them.

Changes

• aqe/execution_plan.rs — new pub(crate) fn reset_locations_on_lost_executor(&self, executor_id) -> Option<usize> on both ExchangeExec and AdaptiveDatafusionExec. Clears shuffle_partitions back to None if any location matches the lost executor; returns the affected stage_id.
• aqe/planner.rs — new pub(super) fn reset_on_lost_executor(&mut self, executor_id) -> Result<HashSet<usize>> on AdaptivePlanner. Walks the live plan tree, calls the per-exec reset, restores runnable_stage_cache / runnable_stage_output for affected stages, re-runs replan_stages(), and returns the set of affected stage_ids.
• aqe/mod.rs — reset_stages_internal now uses the planner's affected set to:
  1. Reset task_infos and transition matching Successful stages back to Running.
  2. Drop any Resolved/Running stages whose embedded plan reads from an affected stage (their ShuffleReaderExec entries hold stale partition locations). The planner regenerates them via actionable_stages once upstream reruns complete.
• aqe/mod.rs — update_task_status now warns (instead of erroring) when a task status arrives for a stage that's no longer in self.stages. This is expected after the dependent-stage drop above.
• Tests — port four executor-failure tests from the static-graph suite into a new aqe/test/executor_failure.rs:
  • test_reset_completed_stage_executor_lost
  • test_reset_resolved_stage_executor_lost
  • test_task_update_after_reset_stage (incl. idempotency check)
  • test_long_delayed_failed_task_after_executor_lost
• Helpers — new test_aqe_aggregation_plan / test_aqe_join_plan helpers in aqe/test/mod.rs that build an AdaptiveExecutionGraph from a SQL-shaped plan, mirroring the static-graph builders.
• Doc cleanup — drop the stale /// - it does not cover executor failure line from the AdaptiveExecutionGraph docstring.

Test Plan

• cargo test -p ballista-scheduler — 76 passed, 0 failed, 1 ignored (pre-existing).
• cargo clippy -p ballista-scheduler --tests — clean.
• cargo fmt -p ballista-scheduler -- --check — clean.
• All four ported tests pass; the static-graph executor-failure tests still pass; existing AQE tests still pass.

Out of Scope

• AQE-specific re-optimization triggered by failure (e.g., switching join strategy after losing data).
• Partial per-partition re-execution beyond what static graph already does.
• Dynamic shuffle coalescing (separate task on the epic).

Refs: #1359

Design and implementation plan committed under docs/superpowers/specs/ and docs/superpowers/plans/.