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/dense_scale.py

@@ -21,7 +21,8 @@ import numpy as np
 from bench.query_set import load_queries, scale_probes
 from bench.report import git_commit
 from bench.run import latency
-from bench.systems import DENSE_MODEL, MODELS, copy_store, machine_facts
+from bench.scratch import copy_store
+from bench.systems import DENSE_MODEL, MODELS, machine_facts
 
 if TYPE_CHECKING:
     from ely_eye.db import Database