feat: enforce DMQ message id

[jpraynaud]

Content

This PR includes a new computation of the DMQ message id, enforcing the strict format specified in CIP-0137.

The message id is now computed as Blake2b_256(msg_body || expires_at.to_be_bytes()), replacing the previous Blake2b_512 digest that also incorporated kes_period.

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • CHANGELOG file is updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • All check jobs of the CI have succeeded
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested

Issue(s)

Relates to #3251

[Copilot]

Pull request overview

This PR updates the DMQ message ID computation to enforce the strict CIP-0137 format by switching to a deterministic Blake2b_256(msg_body || expires_at.to_be_bytes()) digest (removing the previous inclusion of kes_period and changing the hash output size accordingly).

Changes:

• Switched DMQ message ID hashing from Blake2b_512 (including kes_period) to Blake2b_256 over msg_body + big-endian expires_at.
• Added a golden test vector to lock the message ID computation.
• Bumped mithril-dmq crate version and documented the change in CHANGELOG.md.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
internal/mithril-dmq/src/model/builder.rs	Updates message ID computation to CIP-0137 and adds a golden vector test.
internal/mithril-dmq/Cargo.toml	Bumps mithril-dmq version to 0.1.24.
CHANGELOG.md	Records the DMQ message ID format enforcement change.
Cargo.lock	Updates lockfile for the mithril-dmq version bump.

[github-actions]

Test Results

     5 files     203 suites   50m 54s ⏱️
 2 951 tests  2 951 ✅ 0 💤 0 ❌
10 326 runs  10 326 ✅ 0 💤 0 ❌

Results for commit 600492c.

[turmelclem]

LGTM 👍