test: standardize async tests on pytest-asyncio auto mode (#338)

* chore: add pytest-asyncio in auto mode

* test: migrate channel and stream tests to native async

Convert run_async() wrapper tests to plain 'async def test_*' under
pytest-asyncio auto mode. collect_events() in stream_v3_fakes becomes a
coroutine awaited at every call site.

* test: migrate command and model/middleware tests to native async

Convert run_async() wrappers (import, alias, and fixture forms) to plain
'async def test_*'. Multi-call tests merge onto one loop as sequential
awaits; none asserted on loop identity.

* test: migrate TUI, notifier, gateway, and session tests to native async

TUI/notifier/gateway files convert run_async wrappers to plain async
tests. test_sessions.py's unittest.TestCase classes move to
unittest.IsolatedAsyncioTestCase (pytest-asyncio does not await async
methods on plain TestCase; converting blindly would have made ~70 tests
silently vacuous). Its setUpClass keeps a one-shot asyncio.run() since
IsolatedAsyncioTestCase has no async class-level hook. TestLoadingWidget
in test_tui_widgets.py drops its TestCase base for the same reason.

* test: replace direct asyncio.run() calls with native async tests

Convert tests that called asyncio.run() (directly or via a local _run
helper) to plain 'async def test_*'; delete the local helpers.

* test: drop undeclared anyio markers and delete run_async helper

The @pytest.mark.anyio tests relied on anyio being a transitive dep of
httpx; auto-mode pytest-asyncio collects them natively. run_async() and
its fixture are unreferenced after the migration, so remove them —
pytest-asyncio's per-test loop teardown covers the pending-task
cancellation the helper existed for (verified: full suite runs with no
'Event loop is closed' errors or destroyed-task warnings).

tests/test_current_command.py

@@ -2,11 +2,9 @@
 
 from unittest.mock import MagicMock
 
-from tests.conftest import run_async as _run
-
 
 class TestCurrentCommand:
-    def test_prints_thread_workspace_and_memory(self):
+    async def test_prints_thread_workspace_and_memory(self):
         from EvoScientist.commands.base import CommandContext
         from EvoScientist.commands.implementation.general import CurrentCommand
 
@@ -17,14 +15,14 @@ class TestCurrentCommand:
             ui=ui,
             workspace_dir="/tmp/ws",
         )
-        _run(CurrentCommand().execute(ctx, []))
+        await CurrentCommand().execute(ctx, [])
         # Three append_system calls: Thread, Workspace, Memory dir.
         calls = [c.args[0] for c in ui.append_system.call_args_list]
         assert any("Thread: abc123" in s for s in calls)
         assert any("Workspace:" in s for s in calls)
         assert any("Memory dir:" in s for s in calls)
 
-    def test_skips_workspace_when_none(self):
+    async def test_skips_workspace_when_none(self):
         from EvoScientist.commands.base import CommandContext
         from EvoScientist.commands.implementation.general import CurrentCommand
 
@@ -35,7 +33,7 @@ class TestCurrentCommand:
             ui=ui,
             workspace_dir=None,
         )
-        _run(CurrentCommand().execute(ctx, []))
+        await CurrentCommand().execute(ctx, [])
         calls = [c.args[0] for c in ui.append_system.call_args_list]
         assert any("Thread: abc123" in s for s in calls)
         assert not any("Workspace:" in s for s in calls)