Quorum v0.5.1

What's Changed

• feat: per-agent token usage tracking + composer context gauge by @alchaplinsky in #165
• ci: cache apt packages in rust-test job by @alchaplinsky in #166
• chore: bump version to 0.5.1 by @alchaplinsky in #167

Full Changelog: v0.5.0...v0.5.1