feat: derive Eq and Hash trait for messages where possible

[caspermeijn]

Integer and bytes types can be compared using trait Eq. Some generated Rust structs can also have this property by deriving the Eq trait.

Automatically derive Eq and Hash for:

• messages that only have fields with integer or bytes types
• messages where all field types also implement Eq and Hash
• the Rust enum for one-of fields, where all fields implement Eq and Hash

Generated code for Protobuf enums already derives Eq and Hash.

BREAKING CHANGE: prost-build will automatically derive trait Eq and trait Hash for types where all field support those as well. If you manually impl Eq and/or impl Hash for generated types, then you need to remove the manual implementation. If you use type_attribute to derive(Eq) and/or derive(Hash), then you need to remove those.

[caspermeijn]

LGTM, would it make sense to make these derives optional?

I think you mean something like skip_debug but for these traits. I feel like always implementing Eq is acceptable, as that is also the case for PartialEq.

The disadvantage of a skip function is that the complexity is raised in the code generator.

[LucioFranco]

Yeah, I was thinking it may help for those backward compat issues.