test(benchmarks): add concept-search tasks

Three tasks whose target code shares no vocabulary with the prompt, run in a
repository with generated distractor modules.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/benchmarks/tasks/11-search-expired-evaluation/repo/app/accounts.py

@@ -0,0 +1,9 @@
+from dataclasses import dataclass, field
+from datetime import date
+
+
+@dataclass
+class Account:
+    tier: str  # "evaluation" or "paid"
+    evaluation_until: date | None = None
+    entries: list = field(default_factory=list)