Speed up integration tests by reducing subprocess spawning

[evalstate]

…xtures

This commit improves integration test performance by reducing FastAgent instance creation overhead. The main optimization is implementing module-scoped fixtures for FastAgent instances, which significantly reduces test execution time.

Key changes:

1. Module-scoped FastAgent fixtures (conftest.py):

   • Added fast_agent_module, markup_fast_agent_module, and auto_sampling_off_fast_agent_module fixtures
   • These create a single FastAgent instance per test module
   • Function-scoped wrappers (fast_agent, markup_fast_agent, auto_sampling_off_fast_agent) reuse the module-scoped instances
   • AsyncEventBus cleanup (autouse fixture) ensures test isolation

2. Benefits:

   • Reduces FastAgent initialization from 38+ times to ~11-13 times
   • Avoids repeated config loading and MCP server initialization
   • Expected speedup: 2-3x for API integration tests
   • Maintains test isolation through AsyncEventBus reset

3. ACP tests remain unchanged:

   • ACP subprocess tests continue to spawn per-test (37 tests)
   • Module-scoped async fixtures were too complex with pytest-asyncio
   • Per-test isolation is more important for subprocess tests

4. Linting fixes:

   • Removed unused pytest_asyncio imports
   • Fixed unused session_id variables in filesystem tests

All integration tests pass with these changes.