prost-types: Implement Eq for Any and Duration

[theduke]

Manually implement the Eq trait for the Any and Duration well-known types.

These types only contain fields that are themselfes Eq.

[theduke]

It looks like protobuf.rs is auto-generated, but I couldn't find a script or similar that does this, so I just added the impls in lib.rs

[LucioFranco]

@theduke the code is auto generated in the bootstrap test under tests.

[danburkert]

Another way to do this is by injecting the derive impls into the generated code via https://github.com/tokio-rs/prost/blob/master/tests/src/bootstrap.rs#L23 and type_attribute().