Documentation: Deprecation warnings

[felix314159]

There currently are two deprecation warnings:

• pkg_resources is deprecated as an API
• Pydantic json_encoders is deprecated, check out alternatives and the Pydantic V2 migration guide

[fselmo]

• PydanticDeprecatedSince20: Support for class-based config is deprecated, use ConfigDict instead. Deprecated in Pydantic V2.0 to be removed in V3.0. See Pydantic V2 Migration Guide at https://errors.pydantic.dev/2.11/migration/
• execution-spec-tests/src/ethereum_test_fixtures/blockchain.py:182: PydanticDeprecatedSince211: Accessing the 'model_fields' attribute on the instance is deprecated. Instead, you should access this attribute from the model class. Deprecated in Pydantic V2.11 to be removed in V3.0. for field in self.model_fields: