Replaced our embeds of foopb.UnimplementedFooServer with
foopb.UnsafeFooServer. Per the grpc-go docs this reduces the "forwards
compatibility" of our implementations, but that is only a concern for
codebases that are implementing gRPC interfaces maintained by third
parties, and which want to be able to update those third-party
dependencies without updating their own implementations in lockstep.
Because we update our protos and our implementations simultaneously, we
can remove this safety net to replace runtime type checking with
compile-time type checking.
However, that replacement is not enough, because we never pass our
implementation objects to a function which asserts that they match a
specific interface. So this PR also replaces our reflect-based unittests
with idiomatic interface assertions. I do not view this as a perfect
solution, as it relies on people implementing new gRPC servers to add
this line, but it is no worse than the status quo which relied on people
adding the "TestImplementation" test.
Fixes https://github.com/letsencrypt/boulder/issues/7497
b92581d620