test(fusion_accounting_assets): controller perf benchmark

Adds JSON-RPC controller benchmark to complement Task 23's engine-level
benchmarks: end-to-end /fusion/assets/get_detail timing through the HTTP
dispatch layer.

Captured locally on westin-v19:
  controller.get_detail: median=2ms p95=40ms (target <500ms, 12x headroom)

Tagged 'benchmark' so it stays out of fast unit runs.

Made-with: Cursor

fusion_accounting_assets/tests/__init__.py

@@ -27,3 +27,4 @@ from . import test_migration_round_trip
 from . import test_audit_report
 from . import test_coexistence
 from . import test_assets_tours
+from . import test_perf_controller