Add `derive(Eq)` for eligible google types

Hello,

I noticed that in pbjson-types's `google.protobuf.rs`, google types only get the trait `PartialEq`, not `Eq`. Which make impossible to use thes types in a BTreeSet/Map because they require `Ord` and thus `Eq`.

I know that types using floats/double can't use trait `Eq`, but types like `Timestamp` which only uses integers, should have no problem using `derive(Eq)`.

Any chance you can add it to non-float google types ?

Start by inspecting pbjson-types's google.protobuf.rs and tracing how that file is generated. Identify which listed Google types avoid floating-point fields, then add Eq derivation for those types and verify the Rust project builds and its tests pass.

Written by the indexing model from the issue text.