Fix blob schema generation

I was extracting the schema from a model using the now-deprecated `__get_pydantic_core_schema__`. It turns out there's a much simpler way, which is the `__pydantic_core_schema__` property that doesn't raise a warning. I have switched to this, and gotten rid of my deprecation warnings.

Author: rwb27

src/labthings_fastapi/outputs/blob.py

@@ -614,7 +614,7 @@ def __get_pydantic_core_schema__(
         """
         return core_schema.no_info_wrap_validator_function(
             cls._validate,
-            BlobModel.__get_pydantic_core_schema__(BlobModel, handler),
+            BlobModel.__pydantic_core_schema__,
             serialization=core_schema.wrap_serializer_function_ser_schema(
                 cls._serialize,
                 is_field_serializer=False,