client-routes: preserve route state on change events

[dkropachev]

Summary

• limit partial CLIENT_ROUTES_CHANGE merges to configured (connection_id, host_id) pairs
• query all configured connection IDs for changed hosts so the selected route can remain sticky when still present
• include original_port in ClientRoutesEndPoint identity and keep endpoint ordering stable when the port is missing
• update unit coverage and the client-routes integration expectation for changed-host route queries

Closes #846
Closes #813
Closes #850

Testing

• Added unit/integration test coverage for the fixed cases.
• repo-ci fast could not start on this branch due a local repo-ci SQLite shared-memory I/O error: xShmMap method (trying to resize an existing shared-memory segment). GitHub CI should run the normal validation.