Unit tests: update & consistency

This issue is to keep track of unit tests related to the gateway update from OMAP and maintaining consistency between gateways.

- [ ] Test if existing OMAP state was restored locally on start up
- [ ] Test if able to correctly detect OMAP additions
- [ ] Test if able to correctly detect OMAP changes (same key, different value)
- [ ] Test if able to correctly detect OMAP removals
- [ ] Test if OMAP update is sorted properly by key prefix, ignoring keys that aren’t in the prefix list
- [ ] Test if order of RPCs is correct for components to add (bdevs before namespaces, etc)
- [ ] Test if order of RPCs is correct for components to remove (namespaces before bdevs, etc)
- [ ] Test if when watch/notify is enabled, update is called on notify signals
- [ ] Test if after update, local version matches remote version
- [ ] Test if sorted updates for add_namespace contain NSID in value string

The issue names no files or existing test modules. Start by locating the gateway update logic and its unit-test coverage, then work through the OMAP restoration, change detection, sorting, RPC ordering, notification, version matching, and namespace-value cases; done means each listed behavior has a passing test.

Written by the indexing model from the issue text.