JSON alternative for messages format

[secona]

There were some talks about using a JSON alternative, like CBOR, for cargo metadata messages (https://rust-lang.zulipchat.com/#narrow/channel/246057-t-cargo/topic/.60cargo.20metadata.60.20performance/near/476523460). I feel we should try and experiment with it considering our commands rely heavily on serialization and deserialization.

That being said, we may need to wait until the plumbing commands are more complete and things are starting to slowdown.

Love to hear some thoughts. :)

[epage]

On the project goal, we said

Low hanging or egregious bottlenecks may need to be addressed. Otherwise, performance should wait on user feedback.

We likely should wait until we have a full end-to-end cargo check built on plumbing commands so we can benchmark that and see what the impact is.