feat(types): support Python 3.14 in versioned model construction (#1379)

`versioned.py` built its annotation unions by calling
`Union.__getitem__(tuple(...))`. Python 3.14 makes that a descriptor
requiring a `typing.Union` instance, so handing it a tuple raises:

    TypeError: descriptor '__getitem__' requires a 'typing.Union' object
               but received a 'tuple'

`make_versioned_base` and the two annotation-union helpers all called it
that way, so every versioned model fails to build on 3.14. The SDK's
classifiers stop at 3.13 and CI covers 3.10-3.13, so this adds a version
rather than repairing a supported one.

Build the unions with the `|` operator instead, which is the spelling the
project's own lint rules ask for and is equivalent on every supported
version: `functools.reduce(operator.or_, ...)` where the arms come from a
variable-length sequence, and `annotation | None` for the one site that
only ever added `NoneType`. `|` applies the same dedup, nested-union
flattening and `Optional` collapsing as `Union[...]`, so the constructed
annotations are unchanged — verified equal across class, `Any`,
`types.GenericAlias`, `Literal`, `NoneType` and pre-unioned inputs.

`typing.Union` is no longer referenced and leaves the imports.

Clears 10 of the 12 tests that fail on 3.14 and pass on 3.12: all eight
in tests/test_version_scoped_models.py and both
tests/test_account_reference_request_fields.py::test_versioned_*.

Author: KonstantinMirin

src/adcp/types/versioned.py

@@ -16,9 +16,10 @@
 import copy
 import importlib
 import re
-from functools import cache
+from functools import cache, reduce
+from operator import or_
 from types import GenericAlias
-from typing import Any, ClassVar, Literal, Union
+from typing import Any, ClassVar, Literal
 
 from jsonschema.validators import validator_for
 from pydantic import (
@@ -175,7 +176,7 @@ def _fallback_annotation(
         if len(annotations) == 1:
             return annotations[0]
         if annotations:
-            return Union.__getitem__(tuple(annotations))
+            return reduce(or_, annotations)
     all_of = schema.get("allOf")
     if isinstance(all_of, list):
         annotations = [
@@ -191,7 +192,7 @@ def _fallback_annotation(
         annotations = [
             _fallback_annotation({**schema, "type": item}, document, seen) for item in schema_type
         ]
-        return Union.__getitem__(tuple(dict.fromkeys(annotations)))
+        return reduce(or_, dict.fromkeys(annotations))
     if schema_type == "array":
         item_type = _fallback_annotation(schema.get("items", {}), document, seen)
         return GenericAlias(list, item_type)
@@ -483,7 +484,7 @@ class SellerListCreativesRequest(ListCreatives31):
             _fallback_annotation(field_schema, schema),
         )
         if name not in guaranteed_fields:
-            annotation = Union.__getitem__((annotation, type(None)))
+            annotation = annotation | None
         description = field_schema.get("description") if isinstance(field_schema, dict) else None
         if isinstance(field_schema, dict) and "default" in field_schema:
             default = Field(