[Task]: 1.0: Use types generated from protos instead of types.ts

[ishymko]

0.3 spec defined a2a.json JSON Schema which was used to generate types.ts via this script.

1.0 spec states that

SDK language bindings, schemas, and any other derived forms MUST be regenerated from the proto (directly or via code generation) rather than edited manually.

#292 introduced types generated from proto for REST transport with the idea that they could be used as a source of truth in the future in 1.0.

Python SDK already did it in a2aproject/a2a-python#572.

It should use the latest 1.0 proto, so resolving this effectively means supporting 1.0 data model, see the above Python SDK PR and the changelog (note that at the moment of writing this it has inaccuracies, see pending fix a2aproject/A2A#1460).