[IMP] extendable_fastapi: Add generics schemas

Add base schemas to be used to define pagination and paginated results when defining a search method.

extendable_fastapi/readme/newsfragments/380.feature

@@ -0,0 +1,6 @@
+Introduce two new base schemas: `PagedCollection` and `Paging`. These
+schemas are used to describe the structure of a paged collection of
+resources and the paging information parameters that you can use when you
+define a fastapi method that returns a paged collection of resources.
+These schemas are similar to the ones defined in the Odoo's **fastapi** addon
+but works as/with extendable models.

extendable_fastapi/schemas.py

@@ -1,3 +1,5 @@
+from typing import Generic, TypeVar
+
 from extendable_pydantic import ExtendableBaseModel
 
 
@@ -11,7 +13,7 @@ class StrictExtendableBaseModel(
     An ExtendableBaseModel with strict validation.
 
     By default, Pydantic does not revalidate instances during validation, nor
-    when the data is changed. Validation only occurs when the model is created.
+    when the data are changed. Validation only occurs when the model is created.
     This is not suitable for a REST API, where the data is changed after the
     model is created or the model is created from a partial set of data and
     then updated with more data. This class enforces strict validation by
@@ -24,3 +26,28 @@ class StrictExtendableBaseModel(
     * validate_assignment=True: revalidate the model when the data is changed (default is False)
     * extra="forbid": Forbid any extra attributes (default is "ignore")
     """
+
+
+T = TypeVar("T")
+
+
+class PagedCollection(StrictExtendableBaseModel, Generic[T]):
+    """A paged collection of items"""
+
+    # This is a generic model. The type of the items is defined by the generic type T.
+    # It provides you a common way to return a paged collection of items of
+    # extendable models. It's based on the StrictExtendableBaseModel to ensure
+    # a strict validation when used within the odoo fastapi framework.
+
+    total: int
+    items: list[T]
+
+
+class Paging(StrictExtendableBaseModel):
+    """Paging parameters
+
+    By default, the limit is set to 80. To disable the limit set it to null.
+    """
+
+    limit: int | None = 80
+    offset: int = 0