ensure tz on deserialize timestamp

this is needed to ensure we get a utc datetime when reading from sqlite or engines that don't support storing timestamps with a timezone

tests/test_sql_store.py

@@ -0,0 +1,88 @@
+import pytest
+from datetime import datetime, timezone
+from sqlmodel import Session, select
+from ell.stores.sql import SQLStore, SerializedLMP
+from sqlalchemy import Engine, create_engine
+
+from ell.types import utc_now
+
+@pytest.fixture
+def in_memory_db():
+    return create_engine("sqlite:///:memory:")
+
+@pytest.fixture
+def sql_store(in_memory_db: Engine) -> SQLStore:
+    store = SQLStore("sqlite:///:memory:")
+    store.engine = in_memory_db
+    SerializedLMP.metadata.create_all(in_memory_db)
+    return store
+
+def test_write_lmp(sql_store: SQLStore):
+    # Arrange
+    lmp_id = "test_lmp_1"
+    name = "Test LMP"
+    source = "def test_function(): pass"
+    dependencies = str(["dep1", "dep2"])
+    is_lmp = True
+    lm_kwargs = '{"param1": "value1"}'
+    version_number = 1
+    uses = {"used_lmp_1": {}, "used_lmp_2": {}}
+    global_vars = {"global_var1": "value1"}
+    free_vars = {"free_var1": "value2"}
+    commit_message = "Initial commit"
+    created_at = utc_now()
+    assert created_at.tzinfo is not None
+
+    # Act
+    sql_store.write_lmp(
+        lmp_id=lmp_id,
+        name=name,
+        source=source,
+        dependencies=dependencies,
+        is_lmp=is_lmp,
+        lm_kwargs=lm_kwargs,
+        version_number=version_number,
+        uses=uses,
+        global_vars=global_vars,
+        free_vars=free_vars,
+        commit_message=commit_message,
+        created_at=created_at
+    )
+
+    # Assert
+    with Session(sql_store.engine) as session:
+        result = session.exec(select(SerializedLMP).where(SerializedLMP.lmp_id == lmp_id)).first()
+        
+        assert result is not None
+        assert result.lmp_id == lmp_id
+        assert result.name == name
+        assert result.source == source
+        assert result.dependencies == str(dependencies)
+        assert result.is_lm == is_lmp
+        assert result.lm_kwargs == lm_kwargs
+        assert result.version_number == version_number
+        assert result.initial_global_vars == global_vars
+        assert result.initial_free_vars == free_vars
+        assert result.commit_message == commit_message
+        # we want to assert created_at has timezone information
+        assert result.created_at.tzinfo is not None
+
+    # Test that writing the same LMP again doesn't create a duplicate
+    sql_store.write_lmp(
+        lmp_id=lmp_id,
+        name=name,
+        source=source,
+        dependencies=dependencies,
+        is_lmp=is_lmp,
+        lm_kwargs=lm_kwargs,
+        version_number=version_number,
+        uses=uses,
+        global_vars=global_vars,
+        free_vars=free_vars,
+        commit_message=commit_message,
+        created_at=created_at
+    )
+
+    with Session(sql_store.engine) as session:
+        count = session.query(SerializedLMP).where(SerializedLMP.lmp_id == lmp_id).count()
+        assert count == 1