[Task]: Research removing buf from build process #706
Description
Currently buf is executed on each build.
Given that the spec isn't going to be updated often after the release 99% of runs will be no-op while it requires more dependencies to install for initial uv sync/uv run pytest. We should consider extracting it into a separate step which is going to be run manually when needed (when new spec update is coming).
BUT: seems like this process is also required currently for a2a.json here. So maybe this file should be committed to the repo same way as the generated code to avoid regenerating each time (now it's in .gitignore).