Add sub-logger pattern to SetRoutes() to eliminate repeated node.id
field calls. Replace raw strings with zf.* constants throughout
the primary routes code for consistent field naming.
Changes:
- Add nlog sub-logger in SetRoutes() with node.id context
- Replace "prefix" with zf.Prefix
- Replace "changed" with zf.Changes
- Replace "newState" with zf.NewState
- Replace "finalState" with zf.FinalState
