Pinned bincode workspace dependency to the exact version =2.0.0-rc.3 …

[bigmark222]

…in Cargo.toml

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Checklist

• Confirmed that cargo run-checks command has been executed.
• Made sure the book is up to date with changes in this PR.

Related Issues/PRs

• Repro: git checkout v0.14.0 && rm Cargo.lock && cargo publish --dry-run -p burn-core fails with E0425 (bincode API change).

Changes

• Pin bincode in burn-core to =2.0.0-rc.3 to prevent Cargo from resolving 2.0.1+, which removes decode_borrowed_from_slice and breaks publish/build when no lockfile is present.
• Scope: 0.14.x line only; minimal change to restore publishability.

Testing

• cargo run-checks
• cargo publish --dry-run -p burn-core (succeeds with the exact pin)

Additional info just for clarity:

• Cargo.lock isn’t used by library consumers; when downstream builds burn-core, Cargo re-resolves deps. Any lock in the repo is ignored.
• cargo publish also re-resolves unless you force --locked. With the lock present it holds bincode at 2.0.0-rc.3, so the break is masked; without it, Cargo picks bincode 2.0.1 and build/publish fails.
• The repro removes Cargo.lock to mirror the published experience: fresh resolution pulls bincode 2.0.1, which lacks decode_borrowed_from_slice, causing E0425.