Fix GetInfo failing with INTERNAL: proto declares it unary but the servicer yields

[SAY-5]

Fixes #67. The proto declares GetInfo as a unary RPC, but DisciplineServer.GetInfo yields, so gRPC gets a generator where it expects a DisciplineProperties message and every call fails with StatusCode.INTERNAL. Changed the servicer to return the message, dropped the matching [0] indexing in the client, updated the two unit tests, and added an integration test that calls get_discipline_info against a real server so the two sides can't drift again.

[chrislupp]

Thanks for the PR! Two things before I can review this properly:

• Could you retarget this to develop instead of main? We merge all changes there first, as main is reserved for releases. (Sorry, don't have a CONTRIBUTING.md yet spelling this out. Contributions so far have mostly come from people already close to the project, so it hasn't come up. Will be adding one soon.)
• Out of curiosity, how did you come across this issue? Just want to understand a bit about how contributors are finding us.

Once it's retargeted I'll take a proper look at the fix.

[SAY-5]

Retargeted to develop. On discovery: I was searching open GitHub issues around gRPC servicer bugs and this one stood out because the unary/streaming mismatch had a clear repro.

[chrislupp]

Closing this as it was also addressed in #69. Thanks for the retarget and context.