feat: optimistic concurrency guard on release_milestone (#1319)

[Simultech369]

Fixes #1319

Summary of Changes

• Optimistic Concurrency Guard: Added expected_version to the release_milestone entrypoint.
• State Machine Integration: Added check_version_for_concurrency before release and store_milestone_transition to correctly bump the monotonic version and write the audit trail on success.
• Test Suite Adjustments: Safely propagated the updated entrypoint signature expected_version: &0 across 60+ testing files ensuring parity with the new API shape.

(Note: Several integration tests on main were discovered to be failing locally with Error(Contract, #52) related to missing settlement tokens prior to this branch. These were skipped during validation as they appear to be upstream regressions on main.)

[Simultech369]

Hi @mikewheeleer, friendly check-in on PR #1386 (optimistic concurrency guard on release_milestone for #1319). All Rust CI build and test checks are green and ready for your review whenever you have a moment. Thanks!