Workaround misleading metaclass conflict mypy errors

Fix hundreds of errors reported by mypy since 0.990, e.g.:

```
lib/galaxy/model/__init__.py:9626: error: Metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases  [misc]
    class CleanupEventLibraryAssociation(Base):
    ^
```

It should be possible to revert this workaround once
python/mypy#14182 is fixed.

lib/galaxy/model/__init__.py

@@ -97,7 +97,6 @@
     relationship,
 )
 from sqlalchemy.orm.collections import attribute_mapped_collection
-from sqlalchemy.orm.decl_api import DeclarativeMeta
 from sqlalchemy.sql import exists
 from typing_extensions import Protocol
 
@@ -176,6 +175,12 @@
 
 
 if TYPE_CHECKING:
+    # Workaround for https://github.com/python/mypy/issues/14182
+    from sqlalchemy.orm.decl_api import DeclarativeMeta as _DeclarativeMeta
+
+    class DeclarativeMeta(_DeclarativeMeta, type):
+        pass
+
     from galaxy.datatypes.data import Data
     from galaxy.tools import DefaultToolState
     from galaxy.workflow.modules import WorkflowModule
@@ -185,6 +190,8 @@ class _HasTable:
         __table__: Table
 
 else:
+    from sqlalchemy.orm.decl_api import DeclarativeMeta
+
     _HasTable = object
 
 

lib/galaxy/model/tool_shed_install/__init__.py

@@ -23,7 +23,6 @@
     registry,
     relationship,
 )
-from sqlalchemy.orm.decl_api import DeclarativeMeta
 
 from galaxy.model.custom_types import (
     MutableJSONType,
@@ -40,11 +39,18 @@
 mapper_registry = registry()
 
 if TYPE_CHECKING:
+    # Workaround for https://github.com/python/mypy/issues/14182
+    from sqlalchemy.orm.decl_api import DeclarativeMeta as _DeclarativeMeta
+
+    class DeclarativeMeta(_DeclarativeMeta, type):
+        pass
 
     class _HasTable:
         table: Table
 
 else:
+    from sqlalchemy.orm.decl_api import DeclarativeMeta
+
     _HasTable = object
 
 

lib/tool_shed/webapp/model/__init__.py

@@ -33,7 +33,6 @@
     registry,
     relationship,
 )
-from sqlalchemy.orm.decl_api import DeclarativeMeta
 
 import tool_shed.repository_types.util as rt_util
 from galaxy import util
@@ -60,11 +59,18 @@
 WEAK_HG_REPO_CACHE: Mapping["Repository", Any] = weakref.WeakKeyDictionary()
 
 if TYPE_CHECKING:
+    # Workaround for https://github.com/python/mypy/issues/14182
+    from sqlalchemy.orm.decl_api import DeclarativeMeta as _DeclarativeMeta
+
+    class DeclarativeMeta(_DeclarativeMeta, type):
+        pass
 
     class _HasTable:
         table: Table
 
 else:
+    from sqlalchemy.orm.decl_api import DeclarativeMeta
+
     _HasTable = object