…ing (#10769)

… 3.9 (#10972)

For Python < 3.10, we define `EllipsisType = type(Ellipsis)` in
`_typing_extra`. `EllipsisType` is then used in a type expression
but pyright raises an error because `EllipsisType` is defined as
variable.

Instead, we make use of the `ellipsis` builtin, only available
for type checkers (defined in typeshed) as a compatibility hack.

Because we make use of `@dataclass_transform()`, the method is synthesized by type checkers already. This fixes an issue with mypy and the Pydantic plugin, as the plugin removes the `dataclass_transform` spec from `BaseModel` subclasses, but not for `RootModel` which uses a different metaclass, and led to override issues with the synthesized `__replace__` for root models and the `BaseModel.__replace__` definition.

Co-authored-by: Victorien <65306057+Viicos@users.noreply.github.com>

…10989)

…PlainSerializer` and `WrapSerializer` functions (#11008)

…avior (#11027)

…11034)