ci(release): switch crates.io publish to Trusted Publishing (OIDC)

[dkijania]

Summary

Removes the long-lived CARGO_REGISTRY_TOKEN dependency on the publish job. Authentication flows through GitHub Actions OIDC: rust-lang/crates-io-auth-action exchanges the short-lived OIDC token for a single-use crates.io API token, scoped to this workflow + ref.

Existing structure preserved: test → publish-dry-run → publish (gated by the crates-io GitHub Environment). Only the publish step changes.

What this PR changes

• id-token: write permission scoped to the publish job (the other jobs don't need OIDC).
• New auth step before cargo publish using rust-lang/crates-io-auth-action@v1.
• Its output token threaded into CARGO_REGISTRY_TOKEN for the publish step.
• No change to triggers, environment gating, or the test/dry-run jobs.

Prereqs before merging

Both are one-time actions. They don't block the merge itself — but the next release after this lands will fail at the auth step unless these are in place.

• Configure trusted publisher. On https://crates.io/crates/mina-sdk → Settings → Trusted Publishers → Add GitHub Actions:
  • org: `MinaProtocol`
  • repo: `mina-sdk-rust`
  • workflow: `release.yml`
  • environment: `crates-io` (matches the existing job's `environment:` declaration)
• Add team co-owner so the crate is owned by the org, not a single user:
  ```
  cargo owner --add github:o1-labs:eng mina-sdk
  ```
  Currently the crate is sole-owned by `dkijania` — adding the team gives the rest of o1-labs/eng publish rights.

Why

• Bus factor. Today the crate has a single owner and a single token. Team ownership + OIDC means publishes survive maintainer turnover.
• Secret reduction. No `CARGO_REGISTRY_TOKEN` rotation. The auth action mints a token scoped to one publish, then it expires.
• Symmetric. Same change just landed for the sibling `mina-archive-sdk` crate (o1-labs/mina-archive-sdk-rust#1).

After OIDC publishing has succeeded once, the existing `CARGO_REGISTRY_TOKEN` repo secret can be revoked (or kept as a dormant fallback — this workflow no longer reads it).

🤖 Generated with Claude Code