function GrpcServer.add
Attach a service. The argument is the value returned by a
<ServiceName>Service(...) constructor from one of the @bazel//proto/*.axl modules. Raises if a service for the same proto path is already attached.
function GrpcServer.serve
Bind the endpoint synchronously and spawn the accept loop on the global tokio runtime. Returns a [
GrpcServerHandle].
Raises immediately on bind failure (port in use, missing parent dir
for unix socket, etc.). Subsequent add calls on this server raise.
