[x] Add support for custom ProtoBuf options in interceptors and server-side RPCs (closes #8)
[ ] Add Java support through class-bridges (with multimode, closes #10)
[ ] Add support for other request types such as metadata push and fire-and-forget through annotation type (closes #9)
[x] Add support for ProtoBuf builtin types (they're already supported by generating regular classes, but I think we need some kind of bridge with types from like kotlinx.datetime, closes #11)
TODO