import pydantic objects from the _pydantic_compat module (#17667)

This PR changes `from pydantic import BaseModel` to `from
synapse._pydantic_compat import BaseModel` (as well as `constr`,
`conbytes`, `conint`, `confloat`).

It allows `check_pydantic_models.py` to mock those pydantic objects only
in the synapse module, and not interfere with pydantic objects in
external dependencies.

This should solve the CI problems for #17144, which breaks because
`check_pydantic_models.py` patches pydantic models from
[scim2-models](https://scim2-models.readthedocs.io/).

/cc @DMRobertson @gotmax23
fixes #17659 


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scripts-dev/check_pydantic_models.py

@@ -45,7 +45,6 @@ import traceback
 import unittest.mock
 from contextlib import contextmanager
 from typing import (
-    TYPE_CHECKING,
     Any,
     Callable,
     Dict,
@@ -57,30 +56,17 @@ from typing import (
 )
 
 from parameterized import parameterized
-
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import (
-        BaseModel as PydanticBaseModel,
-        conbytes,
-        confloat,
-        conint,
-        constr,
-    )
-    from pydantic.v1.typing import get_args
-else:
-    from pydantic import (
-        BaseModel as PydanticBaseModel,
-        conbytes,
-        confloat,
-        conint,
-        constr,
-    )
-    from pydantic.typing import get_args
-
 from typing_extensions import ParamSpec
 
+from synapse._pydantic_compat import (
+    BaseModel as PydanticBaseModel,
+    conbytes,
+    confloat,
+    conint,
+    constr,
+    get_args,
+)
+
 logger = logging.getLogger(__name__)
 
 CONSTRAINED_TYPE_FACTORIES_WITH_STRICT_FLAG: List[Callable] = [
@@ -183,22 +169,16 @@ def monkeypatch_pydantic() -> Generator[None, None, None]:
         # Most Synapse code ought to import the patched objects directly from
         # `pydantic`. But we also patch their containing modules `pydantic.main` and
         # `pydantic.types` for completeness.
-        patch_basemodel1 = unittest.mock.patch(
-            "pydantic.BaseModel", new=PatchedBaseModel
+        patch_basemodel = unittest.mock.patch(
+            "synapse._pydantic_compat.BaseModel", new=PatchedBaseModel
         )
-        patch_basemodel2 = unittest.mock.patch(
-            "pydantic.main.BaseModel", new=PatchedBaseModel
-        )
-        patches.enter_context(patch_basemodel1)
-        patches.enter_context(patch_basemodel2)
+        patches.enter_context(patch_basemodel)
         for factory in CONSTRAINED_TYPE_FACTORIES_WITH_STRICT_FLAG:
             wrapper: Callable = make_wrapper(factory)
-            patch1 = unittest.mock.patch(f"pydantic.{factory.__name__}", new=wrapper)
-            patch2 = unittest.mock.patch(
-                f"pydantic.types.{factory.__name__}", new=wrapper
+            patch = unittest.mock.patch(
+                f"synapse._pydantic_compat.{factory.__name__}", new=wrapper
             )
-            patches.enter_context(patch1)
-            patches.enter_context(patch2)
+            patches.enter_context(patch)
         yield