Publish barretenberg-rs to crates.io #1627

Context

PR AztecProtocol/aztec-packages#20496 added the release infrastructure for barretenberg-rs.

Steps

• Do first manual cargo publish of barretenberg-rs (published 4.0.0-nightly.20260218)
• Create AztecProtocol/crates-io-owners GitHub team (members: johnathan79717, AztecBot)
• Add github:AztecProtocol:crates-io-owners as a crate owner (blocked: need to install crates.io GitHub App on the org)
• Add AztecBot as individual crate owner (blocked: AztecBot needs to sign into crates.io once to create an account)
• Add CARGO_REGISTRY_TOKEN in CI secrets (GitHub Actions master environment)

Notes

• Crate is live: https://crates.io/crates/barretenberg-rs
• Nightlies and stable releases will both publish to crates.io
• ci-release-pr test tags (e.g. v0.0.1-commit.<hash>) will also publish — this is fine as crates.io supports semver prereleases
• Current CARGO_REGISTRY_TOKEN is scoped to johnathan79717 — should eventually migrate to AztecBot's token