Add variable-m DP-SAA and reproducible benchmarks

[ila]

Summary

• add a disjoint variable-m SAA path for powers of two above 64 while preserving the optimized 64-bit path
• extend DP-SAA aggregation and rewrite support, including per-aggregate bounds, rescaling controls, DISTINCT handling, and non-empty-lane SUM/AVG releases
• consolidate the TPC-H and ClickBench paper benchmarks into standalone, configuration-driven workflows with archived figure inputs and reproducibility documentation
• remove obsolete PAC/JCC-H benchmark workflows and generated benchmark artifacts

Validation

• built as_tpch_benchmark, as_clickbench_benchmark, and dp_benchmark_runner
• passed the focused DP-SAA, variable-m, stability, and DP-standard SQL tests during development
• validated every paper utility configuration with --dry-run
• completed a one-run TPC-H SF30 Q01 sanity check for m=64 and m=512, including runtime and diagnostic passes
• regenerated the archived Q01 AVG, stability, SAA m, and AS m figure summaries from their raw CSV inputs

See repro.md for the experiment matrix, build/run commands, metrics, bounds, and figure regeneration commands.