fix: use naive UTC timestamps for Message and Conversation creation

[hyhyf]

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Summary

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[hyhyf]

#38553

[github-actions]

Pyrefly Diff

base → PR

--- /tmp/pyrefly_base.txt	2026-07-09 03:32:14.540782885 +0000
+++ /tmp/pyrefly_pr.txt	2026-07-09 03:31:58.755722289 +0000
@@ -4303,21 +4303,21 @@
 ERROR Argument `SimpleNamespace` is not assignable to parameter `db_provider` with type `MCPToolProvider` in function `core.entities.mcp_provider.MCPProviderEntity.from_db_model` [bad-argument-type]
   --> tests/unit_tests/core/entities/test_entities_mcp_provider.py:60:46
 ERROR `None` is not subscriptable [unsupported-operation]
-   --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:808:12
+   --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:807:12
 ERROR Argument `SimpleNamespace` is not assignable to parameter `credential_record` with type `ProviderCredential | ProviderModelCredential` in function `core.entities.provider_configuration.ProviderConfiguration._update_load_balancing_configs_with_credential` [bad-argument-type]
-    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1036:31
+    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1035:31
 ERROR Argument `SimpleNamespace` is not assignable to parameter `credential_record` with type `ProviderCredential | ProviderModelCredential` in function `core.entities.provider_configuration.ProviderConfiguration._update_load_balancing_configs_with_credential` [bad-argument-type]
-    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1055:27
+    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1054:27
 ERROR `None` is not subscriptable [unsupported-operation]
-    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1171:12
+    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1170:12
 ERROR `None` is not subscriptable [unsupported-operation]
-    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1172:12
+    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1171:12
 ERROR `None` is not subscriptable [unsupported-operation]
-    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1188:12
+    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1187:12
 ERROR `None` is not subscriptable [unsupported-operation]
-    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1702:12
+    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1699:12
 ERROR `None` is not subscriptable [unsupported-operation]
-    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1894:12
+    --> tests/unit_tests/core/entities/test_entities_provider_configuration.py:1891:12
 ERROR Object of class `ModuleType` has no attribute `MockExtension` [missing-attribute]
   --> tests/unit_tests/core/extension/test_extensible.py:62:9
 ERROR Cannot index into `OrderedDict[str, ModuleExtension]` [bad-index]

[github-actions]

Pyrefly Type Coverage

Metric	Base	PR	Delta
Type coverage	52.59%	52.59%	0.00%
Strict coverage	52.11%	52.11%	0.00%
Typed symbols	32,538	32,538	0
Untyped symbols	29,605	29,605	0
Modules	2982	2982	0