rust: Upgrade to format-bytes 0.3
This removes use of the proc-macro-hack crate, which is possible now that
we don’t support Rust 1.41 to 1.44 anymore.
This in turn fixes spurious errors reported by rust-analyser:
https://github.com/rust-analyzer/rust-analyzer/issues/9606#issuecomment-919240134
Differential Revision: https://phab.mercurial-scm.org/D11938
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