Keep the ablation arms inside the line budget the repo enforces

copy_store() moved into bench/scratch.py: systems.py had reached 512 lines
and bench/filesize_check fails anything over 500. The move is behaviour
identical, so the scale reports keep the commit stamp they were generated
against — the code they describe is complete at that commit.

bench/scale_check.py

@@ -17,7 +17,8 @@ from typing import Any
 from bench.query_set import load_queries, scale_probes
 from bench.report import git_commit
 from bench.run import latency
-from bench.systems import copy_store, machine_facts
+from bench.scratch import copy_store
+from bench.systems import machine_facts
 
 DEFAULT_HOME = Path("bench/runs/baseline")
 DEFAULT_SCRATCH = Path("bench/runs/scale")