feat: add A2ABaseModel (#292)

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Fixes #291 🦕

---------

Signed-off-by: Shingo OKAWA <[email protected]>
Co-authored-by: Mike Smith <[email protected]>

Author: ognis1205

scripts/generate_types.sh

@@ -32,6 +32,7 @@ uv run datamodel-codegen \
   --use-one-literal-as-default \
   --class-name A2A \
   --use-standard-collections \
-  --use-subclass-enum
+  --use-subclass-enum \
+  --base-class a2a._base.A2ABaseModel
 
 echo "Codegen finished successfully."

src/a2a/_base.py

@@ -0,0 +1,15 @@
+from pydantic import BaseModel, ConfigDict
+
+
+class A2ABaseModel(BaseModel):
+    """Base class for shared behavior across A2A data models.
+
+    Provides a common configuration (e.g., alias-based population) and
+    serves as the foundation for future extensions or shared utilities.
+    """
+
+    model_config = ConfigDict(
+        # SEE: https://docs.pydantic.dev/latest/api/config/#pydantic.config.ConfigDict.populate_by_name
+        validate_by_name=True,
+        validate_by_alias=True,
+    )