Rust bindings: add typical impls

[paulhauner]

Thanks again for this great library!

When implementing blst in Lighthouse (Eth2 impl) I noticed that the core structs (e.g., PublicKey, Signature, etc) are missing some typical and useful impls. In particular:

• Clone
• PartialEq
• Eq (if it adheres to the definition here)

As you can see in our code, I've added some wrapper structs to Lighthouse and made my own custom implementations. It would be great if these were included in the library by default.

If the implementations I've used (see previous link) are good, I'm happy to make a PR to this repository. However I suspect that you might know faster or more elegant ways to achieve these things.

[dot-asm]

However I suspect that you might know faster or more elegant ways to achieve these things.

Don't be so sure:-) PR is welcomed!

[sean-sn]

Closing the issue since the merged PR resolved it

[tessico]

Any reason why PartialEq was not added for SecretKey? Is this some security concern or just an omission?
I wonder what the best practice is, e.g. RustCrypto's signatures crates have explicit PartialEq impl for their dsa and ecdsa crates.

[dot-asm]

I wonder what the best practice is, e.g. RustCrypto's signatures crates have explicit PartialEq impl for their dsa and ecdsa crates.

Formally speaking this is not exactly a right place to pop such a question. As we are not considering ourselves as a "Rust shop." We do exercise, and one might even say advocate for minimally-required principle though. Taking this question as an example. You are not supposed to use your secret key for anything but signing, so why would it require a comparison trait? One can make a legitimate case against attaching generic traits as they make no commitments to constant-time execution, while blst does...