add: PostgreSQL 支持（asyncpg 驱动，from_url/from_config + 集成测试）

tests/test_database.py

@@ -0,0 +1,39 @@
+"""Database 构造与 from_config 的纯 API 校验（无 IO）。"""
+
+import pytest
+
+from chongming_database import Database
+
+
+async def test_constructor_requires_exactly_one_arg():
+    # 两个都不给
+    with pytest.raises(ValueError):
+        Database()
+    # 两个都给
+    with pytest.raises(ValueError):
+        Database("x.db", url="postgresql+asyncpg://localhost/db")
+
+
+async def test_from_config_sqlite_requires_path():
+    with pytest.raises(ValueError):
+        Database.from_config({"type": "sqlite"})
+
+
+async def test_from_config_postgres_requires_url():
+    with pytest.raises(ValueError):
+        Database.from_config({"type": "postgresql"})
+
+
+async def test_from_config_unsupported_type():
+    with pytest.raises(NotImplementedError):
+        Database.from_config({"type": "mysql", "url": "mysql://localhost/db"})
+
+
+async def test_postgres_url_normalized_to_asyncpg():
+    db = Database.from_url("postgresql://user:pwd@127.0.0.1:5432/mydb")
+    assert db._build_url() == "postgresql+asyncpg://user:pwd@127.0.0.1:5432/mydb"
+
+
+async def test_explicit_driver_url_untouched():
+    db = Database(url="postgresql+asyncpg://user:pwd@127.0.0.1:5432/mydb")
+    assert db._build_url() == "postgresql+asyncpg://user:pwd@127.0.0.1:5432/mydb"