feat(mdk-core): add GREASE support for MLS protocol extensibility (#142)

* feat(mdk-core): add GREASE support for MLS protocol extensibility

Add support for GREASE (Generate Random Extensions And Sustain Extensibility)
as defined in RFC 9420 Section 13.5. This ensures implementations correctly
handle unknown values and maintains protocol forward compatibility.

- Update OpenMLS dependencies to git main branch for GREASE support
- Add GREASE injection to capabilities (ciphersuites, extensions, proposals,
  credentials) via OpenMLS's Capabilities::with_grease()
- Add comprehensive tests for GREASE value injection
- Add refinery-core dependency to handle OpenMLS migration errors

Fixes #26

* docs: add PR #142 reference to changelog entries

* chore: upgrade refinery from 0.8 to 0.9 to align with OpenMLS

- Remove refinery-core dependency (no longer needed)
- Remove RefineryCore error variant from mdk-sqlite-storage
- Both MDK and OpenMLS now use the same refinery version

Author: erskingardner