Add integration tests for execution persistence, metrics, and opportunity writing

- Implemented integration tests for the execution writer to ensure trade orders and PnL are persisted correctly.
- Created integration tests for the metrics calculator to summarize execution data accurately.
- Added integration tests for the opportunity writer to verify event persistence.
- Established PostgreSQL schema validation tests to ensure all expected tables, columns, and constraints exist.
- Removed outdated unit tests that relied on DuckDB and replaced them with tests using PgStore.

tests/unit/test_config_repositories.py

@@ -8,7 +8,7 @@ from arbitrade.config.service import (
     ConfigPairing,
     ConfigSetting,
 )
-from arbitrade.storage.db import DuckDBStore
+from arbitrade.storage.pg_store import PgStore
 from arbitrade.storage.repositories import (
     ConfigBacktestingDefaultsRepository,
     ConfigPairingRepository,
@@ -19,7 +19,7 @@ from arbitrade.storage.repositories import (
 @pytest.fixture
 def mock_store():
     """Create a mock database store."""
-    store = Mock(spec=DuckDBStore)
+    store = Mock(spec=PgStore)
     return store
 
 
@@ -244,7 +244,8 @@ def test_config_pairing_repository_create_pairing(mock_store):
         ]
 
         # Create pairing
-        pairing = ConfigPairing(base_asset="BTC", quote_asset="USD", enabled=True, source="Kraken")
+        pairing = ConfigPairing(
+            base_asset="BTC", quote_asset="USD", enabled=True, source="Kraken")
 
         result = repo.create_pairing(pairing)