chore: gatekeeper fix race condition in JSON DB

[Bushstar]

• Resolves: Fix race condition in Gatekeeper JSON DB #1021

[Copilot]

Pull Request Overview

This PR addresses a race condition in the JSON database implementation by adding mutex-like concurrency control and improves error handling for malformed DIDs.

• Added exclusive execution wrapper to prevent concurrent database operations
• Extracted DID validation logic into a dedicated method with better error handling
• Added test coverage for malformed DID edge case

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/gatekeeper/src/db/abstract-json.ts	Implements concurrency control with runExclusive method and improves DID validation
tests/gatekeeper/utils.test.ts	Adds test case for malformed DID with no suffix

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