chore: prepare dyns v0.6.0-beta.2

[eareimu]

Release prep

Prepare dyns v0.6.0-beta.2 with endpoint candidate lookup changes and beta.2 h3x/dquic dependency contracts.

Draft tag message

# dyns v0.6.0-beta.2

## Changes

- Add endpoint candidate grouping and candidate lookup support.
- Expose endpoint candidates from H3, HTTP, and mDNS resolvers.
- Implement aggregate resolver endpoint candidate lookup.
- Simplify endpoint candidate group types.
- Update DHTTP/QUIC dependency contracts for the beta.2 line.

## Published crate

- `dyns` v0.6.0-beta.2

Release gates

• Target branch: main
• Planned tag: v0.6.0-beta.2
• Initial/incremental: incremental
• Surface: crates.io package dyns + tag-CI GitHub Release

Dependency wait conditions

Wait for h3x v0.6.0-beta.2 to be published and visible on crates.io before final merge/tag readiness. dquic v0.7.0-beta.2 is already published and visible.