feat: add rust-protobuf support to extism-convert

[nilslice]

(code from @zshipko, thank you!)

[dselans]

❤️

[zshipko]

I think the CI failure is because when it's built with --all-features the two Protobuf types conflict

I'm wondering if we should just break the current feature names an use prost to enable the Prost type/prost crate and protobuf to enable the Protobuf type/protobuf crate. It seems like long-term that makes the most sense, even if it's kind of weird for current users right now.

[nilslice]

I'm wondering if we should just break the current feature names an use prost to enable the Prost type/prost crate and protobuf to enable the Protobuf type/protobuf crate. It seems like long-term that makes the most sense, even if it's kind of weird for current users right now.

yea, I agree. I've updated to follow this plan.