chore: pin witnessed close-group dependency branches

[mickvandijke]

Summary

• replace local/registry protocol and core pins with git branch dependencies for the witnessed close-group stack
• keep saorsa-node source behavior unchanged while ensuring it compiles against the updated saorsa-core API

Depends on

• feat(dht): add witnessed close-group lookup saorsa-core#132
• feat: re-export witnessed close-group types ant-protocol#13

Tests

• cargo check --all-targets --all-features
• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings

[jacderida]

Closing as superseded. This PR only re-pins ant-node's saorsa-core/ant-protocol deps to the dev fork/feature branches (mickvandijke/saorsa-core@snp-witnessed-close-group, WithAutonomi/ant-protocol@snp-witnessed-close-group) — a scaffold for building against the witnessed-close-group feature while the upstream PRs were open. It has no source changes.

ant-node's rc-2026.6.2 already pins the canonical saorsa-labs/saorsa-core@rc-2026.6.2 and WithAutonomi/ant-protocol@rc-2026.6.2 refs, which now contain the witnessed feature via saorsa-core #132 and ant-protocol #13. ant-node will pick it up automatically via a lock refresh on the next rc roll (0.12.1-rc.6); no source change here to preserve.