feat: improve test configuration and fixtures

- Add cli to pytest.ini pythonpath for test discovery
- Simplify tests/conftest.py to only mock aitbc_crypto when not importable
- Add minimal aitbc_crypto.signing.ReceiptSigner mock for coordinator imports
- Remove complex test fixtures and collection hooks
- Update pytest.ini with comprehensive pythonpath entries
- Add environment variables for tests
- Add warning filters for common deprecations

pytest.ini

@@ -1,12 +1,47 @@
 [pytest]
-testpaths = tests apps/blockchain-node/tests apps/coordinator-api/tests apps/wallet/tests cli/tests
-python_files = test_*.py
+# pytest configuration for AITBC
+
+# Test discovery
+python_files = test_*.py *_test.py
 python_classes = Test*
 python_functions = test_*
-addopts = -v --tb=short
-asyncio_mode = auto
-asyncio_default_fixture_loop_scope = function
+
+# Custom markers
 markers =
-    slow: marks tests as slow
-    integration: marks tests as integration tests
-    unit: marks tests as unit tests
+    unit: Unit tests (fast, isolated)
+    integration: Integration tests (may require external services)
+    slow: Slow running tests
+
+# Test paths to run
+testpaths = tests/cli apps/coordinator-api/tests/test_billing.py
+
+# Additional options for local testing
+addopts = 
+    --verbose
+    --tb=short
+
+# Python path for imports (must match pyproject.toml)
+pythonpath =
+    .
+    cli
+    packages/py/aitbc-core/src
+    packages/py/aitbc-crypto/src
+    packages/py/aitbc-p2p/src
+    packages/py/aitbc-sdk/src
+    apps/coordinator-api/src
+    apps/wallet-daemon/src
+    apps/blockchain-node/src
+
+# Environment variables for tests
+env =
+    AUDIT_LOG_DIR=/tmp/aitbc-audit
+    DATABASE_URL=sqlite:///./test_coordinator.db
+
+# Warnings
+filterwarnings =
+    ignore::UserWarning
+    ignore::DeprecationWarning
+    ignore::PendingDeprecationWarning
+    ignore::pytest.PytestUnknownMarkWarning
+    ignore::pydantic.PydanticDeprecatedSince20
+    ignore::sqlalchemy.exc.SADeprecationWarning