Dockerfile: bump CADGENBENCH_SHA to ed31274 (parallel evaluate)

Picks up the eval orchestrator's switch to ProcessPoolExecutor across
fixtures (cadgenbench commit ed31274). On the Space's cpu-upgrade
tier (8 vCPU) this should give a near-linear speedup on real-GT-scale
runs; locally on the 5-stub set we saw ~2.4x going from --workers 1
to --workers 4 (1m13s -> 31s). The default worker count is
min(8, os.cpu_count()) so the Space gets the speedup without setting
any env var.

Verified locally: per-fixture cad_score outputs are byte-identical
between sequential and parallel runs (eval is per-fixture independent
+ deterministic).

Dockerfile

@@ -44,7 +44,7 @@ RUN pip install --no-cache-dir playwright \
 
 # cadgenbench from the Public GitHub repo, pinned to a commit. Bumping
 # CADGENBENCH_SHA is the one-line path to picking up a new cadgenbench.
-ARG CADGENBENCH_SHA=1747493
+ARG CADGENBENCH_SHA=ed31274
 RUN pip install --no-cache-dir \
         "cadgenbench @ git+https://github.com/huggingface/cadgenbench.git@${CADGENBENCH_SHA}"