fix: use correct model validator signature (#586)

We had previously been using an incorrect method signature that was
apparently working, but in an undefined way, and pydantic v 2.12 "fixed"
(broke, for us) this -- see "after model validators"
https://pydantic.dev/articles/pydantic-v2-12-release)

Author: jsstevenson

pyproject.toml

@@ -41,6 +41,7 @@ dependencies = [
     "requests",
     "canonicaljson",
     "setuptools>=78.1.0", # TODO remove this pin caused by HGVS issue
+    "typing-extensions",
 ]
 
 [project.optional-dependencies]

src/ga4gh/core/models.py

@@ -14,6 +14,7 @@
     StringConstraints,
     model_validator,
 )
+from typing_extensions import Self
 
 from ga4gh.core.identifiers import GA4GH_IR_REGEXP
 
@@ -216,12 +217,12 @@ class MappableConcept(Element, BaseModelForbidExtra):
     )
 
     @model_validator(mode="after")
-    def require_name_or_primary_coding(cls, v):  # noqa: ANN001 N805 ANN201
+    def require_name_or_primary_coding(self) -> Self:
         """Ensure that ``name`` or ``primaryCoding`` is provided"""
-        if v.primaryCoding is None and v.name is None:
+        if self.primaryCoding is None and self.name is None:
             err_msg = "One of `name` or `primaryCoding` must be provided."
             raise ValueError(err_msg)
-        return v
+        return self
 
 
 Element.model_rebuild()