Support proto v0.47.4

[liby]

The plugin was failing with "invalid type: null, expected a string" error when calling the load_versions function.

❯ proto versions zig
Error: plugin::wasm::failed_function_call

  × invalid type: null, expected a string at line 1 column 151

This was caused by a breaking change in the upstream dependency. Upgrading the proto_pdk dependency resolves this issue.

[konomae]

Thanks for addressing this!