fix: resolve ruff lint errors in benchmark suite

Remove unused imports (shutil, string, datetime, os, yaml, time,
SCALE_CONFIGS) and unused variable assignments in timing-only calls.

tests/benchmarks/test_search_bench.py

@@ -216,7 +216,7 @@ class TestSearchNResultsScaling:
         latencies = []
         for _ in range(5):
             start = time.perf_counter()
-            result = search_memories(
+            search_memories(
                 "authentication middleware", palace_path=palace_path, n_results=n_results
             )
             latencies.append((time.perf_counter() - start) * 1000)