Clean up generated code and implement strip_boilerplate

Remove redundant newlines and duplicate headers from generated files
and prevent the creation of empty sub-modules. Implement the
`strip_boilerplate` function to remove generated headers and
attributes, including a comprehensive test suite.

roto-tonic/src/generated/interop.rs

@@ -1,6 +1,5 @@
 // @generated by protoc-gen-roto — do not edit
 #[allow(unused_imports)]
-
 use roto_runtime::{ProtoAccessor, ProtoBuilder, Result, RotoError, read_varint, RepeatedFieldIterator, RotoMessage};
 use core::str;
 #[cfg(feature = "alloc")]
@@ -407,9 +406,6 @@ impl roto_runtime::RotoMessage for OwnedStreamingResponse {
 }
 
 
-// @generated by protoc-gen-roto — do not edit
-#[allow(unused_imports)]
-
 
 #[cfg(feature = "alloc")]
 use tonic::{Request, Response, Status};