test(dkg): add comprehensive tests for DkgConfig type

[refcell]

Summary

Add comprehensive unit tests for the DkgConfig type in the dkg crate.

Changes

• crates/node/dkg/src/config.rs: Added 13 new unit tests covering:
  • n() method: participant count, single participant, many participants (100)
  • t() method: threshold value, threshold of 1, large threshold (67)
  • my_public_key(): derivation from identity key, consistency across calls, different identities produce different keys
  • Debug implementation verification
  • Clone trait verification
  • Participants vector matches n() return value
  • Threshold boundary case (t == n)

Verification

• All 13 tests pass
• Clippy clean
• Increases test coverage for the DkgConfig configuration type

[refcell]

Duplicate of #65 which was already merged