*Motivation*

The code generation for `repeated long` is not handled properly. (I am not sure how changes were made to PulsarApi.proto)

*Modification*

This pull request adds the code to handle generating code for `repeated long`.

*Test*

Add unit test to ensure `repeated long` is processed. Add test cases to cover both packed and non-package serialization for `repeated long`.

See more details about packed serialization: https://developers.google.com/protocol-buffers/docs/encoding#optional