feature(turborepo): Rust capnproto hashing (#5824)
### Description
Switches the Rust side to capnproto. We're only merging the Rust code so
we can avoid a backlog of stacked PRs while also avoiding the global
hash bump on the Go side.
### Testing Instructions
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Closes TURBO-1272
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Co-authored-by: Alexander Lyon <Alexander Lyon>
Co-authored-by: nicholaslyang <Nicholas Yang>
