fix(actor): repair list_actors lock-filter test fixtures (#8588)

Address CI lint + unit_tests failures on the namespace-lock test suite:

- Step file: drop unused imports (yaml, ExitStack, ValidationError) and
  unused noqa directives flagged by ruff F401/RUF100; rewrite the
  collected-errors list to use iterable unpacking (RUF005); register the
  "I create an ActorLoader with initial actors from multiple namespaces"
  step under both @given and @when so scenario 3 is no longer reported as
  undefined; remove the dead _error_collector inner function the reviewer
  flagged.
- Step regex fix: the concurrent-modifications step pattern ended with
  '' (two single quotes) instead of `` (two backticks), so it never
  matched the feature file's `(triggering ``discover()``)` literal.
- Test fixtures: add the required `description` field to _make_actor_yaml
  in both the BDD step file and tests/actor/test_loader_list_actors_thread_safety.py
  so ActorConfigSchema validation passes (previously every scenario
  errored at discover() with "description: Field required").
- Concurrent worker names: collapse three-slash actor names like
  "conc/ns{i % 2}/concurrent_{i}" to the single-slash form
  "conc/concurrent_{i}" required by the schema's namespaced-name rule.
- Test file: drop unused `yaml` import and three unused F841 assignments
  in _list_worker; apply ruff format.
- Feature file: switch the @issue_8660 TDD tag to @tdd_issue_8588 to
  match the CONTRIBUTING.md tag convention for the bug issue this PR
  closes.

ISSUES CLOSED: #8588

tests/actor/test_loader_list_actors_thread_safety.py

@@ -13,14 +13,13 @@ import threading
 import time
 from pathlib import Path
 
-import yaml
-
 from cleveragents.actor.loader import ActorLoader
 
 
 def _make_actor_yaml(name: str, provider: str = "openai", model: str = "gpt-4") -> str:
     return f"""name: {name}
 type: llm
+description: Test actor {name}
 provider: {provider}
 model: {model}
 tools: []
@@ -60,7 +59,9 @@ class TestListActorsThreadSafety:
             try:
                 for i in range(20):
                     extra_file = root / f"extra_{i}.yaml"
-                    extra_file.write_text(_make_actor_yaml(f"conc/ns{i % 2}/thread_{i}"))
+                    extra_file.write_text(
+                        _make_actor_yaml(f"conc/thread_{i}")
+                    )
                     loader.discover()
                     time.sleep(0.01)
                     if extra_file.exists():
@@ -115,9 +116,9 @@ class TestListActorsThreadSafety:
         def _list_worker() -> None:
             try:
                 for _ in range(30):
-                    all_actors = loader.list_actors()
-                    local = loader.list_actors(namespace="local")
-                    remote = loader.list_actors(namespace="remote")
+                    loader.list_actors()
+                    loader.list_actors(namespace="local")
+                    loader.list_actors(namespace="remote")
                     time.sleep(0.01)
             except Exception as exc:
                 errors.append(exc)
@@ -141,7 +142,9 @@ class TestListActorsThreadSafety:
         def _add_actor() -> None:
             try:
                 for i in range(20):
-                    (root / f"new_{i}.yaml").write_text(_make_actor_yaml(f"conc/new_{i}"))
+                    (root / f"new_{i}.yaml").write_text(
+                        _make_actor_yaml(f"conc/new_{i}")
+                    )
                     loader.discover()
                     time.sleep(0.01)
                     if (root / f"new_{i}.yaml").exists():
@@ -172,4 +175,5 @@ class TestListActorsThreadSafety:
 
 if __name__ == "__main__":  # pragma: no cover
     import pytest
+
     pytest.main([__file__, "-v"])