[http-client-python] import mixin operations from init file (#7992)

When we made mixin operations private, we updated all of our imports to
import from the exact file it was generated in, instead of from the
`operations` module. This makes patch changes to the mixin operation
class via `operations/_patch.py` lose their effect, and was an
unintended consequence. This PR fixes that, importing mixin operation
classes from `operations/__init__.py` so patch changes still take effect

---------

Co-authored-by: iscai-msft <isabellavcai@gmail.com>

Author: iscai-msft

.chronus/changes/python-bumpDeps-2025-6-23-14-5-43.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Import mixins from operations init file to get patch changes

packages/http-client-python/generator/pygen/codegen/models/client.py

@@ -322,13 +322,11 @@ def imports(self, async_mode: bool, **kwargs) -> FileImport:
         )
         serialize_namespace = kwargs.get("serialize_namespace", self.code_model.namespace)
         for og in self.operation_groups:
-            suffix = f".{og.filename}" if (not self.code_model.options["multiapi"]) and og.is_mixin else ""
             file_import.add_submodule_import(
                 self.code_model.get_relative_import_path(
                     serialize_namespace,
                     self.code_model.get_imported_namespace_for_operation(og.client_namespace, async_mode),
-                )
-                + suffix,
+                ),
                 og.class_name,
                 ImportType.LOCAL,
             )

packages/http-client-python/generator/pygen/codegen/serializers/operations_init_serializer.py

@@ -9,6 +9,12 @@
 from ..models import CodeModel, OperationGroup
 
 
+def get_pylint_disable(code_model: CodeModel, og: OperationGroup) -> str:
+    if og.is_mixin and not code_model.options["multiapi"]:
+        return " # pylint: disable=unused-import"
+    return ""
+
+
 class OperationsInitSerializer:
     def __init__(
         self,
@@ -27,9 +33,8 @@ def _get_filename(operation_group: OperationGroup) -> str:
             return "_operations" if self.code_model.options["combine-operation-files"] else operation_group.filename
 
         return [
-            f"from .{_get_filename(og)} import {og.class_name}  # type: ignore"
+            f"from .{_get_filename(og)} import {og.class_name} # type: ignore{get_pylint_disable(self.code_model, og)}"
             for og in self.operation_groups
-            if not og.is_mixin or self.code_model.options["multiapi"]
         ]
 
     def serialize(self) -> str: