zebra: add a new ADJACENCY route type for local neighbors

[mjstapp]

Add a new route type for local neighbors. The neighbor events handled in zebra_neigh.c can (configurably) manage host routes for local neighbors. The routes have a new, distinct route type, so they can be redistributed like any other type. There's a simple topotest also; I'd like to add some more cases to it, but it seems worth opening this PR so we can discuss the approach.

[greptile-apps]

Greptile Summary

This PR adds adjacency host routes for local zebra neighbors. The main changes are:

• A new adjacency route type and netlink protocol mapping.
• Interface CLI and YANG config for host-routes-enable.
• Neighbor add, delete, and config-toggle handling for adjacency host routes.
• RIB helpers for adding and deleting local host routes.
• A new topotest topology for adjacency route redistribution.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
zebra/zebra_neigh.c	Adds neighbor host-route state handling for add, delete, cleanup, and config-toggle paths.
zebra/zebra_rib.c	Adds ADJACENCY route metadata and helpers for local host-route add and delete operations.
zebra/zebra_nb_config.c	Wires the interface host-routes YANG leaf to zebra neighbor route reconciliation.
lib/route_types.txt	Defines the new redistributable adjacency route type and help text.
tests/topotests/adjacency_routes/test_adjacency_routes_topo1.py	Adds a topology test that creates a local neighbor and checks adjacency route visibility.

_{Reviews (2): Last reviewed commit: "zebra: remove some headers from zebra_ne..." | Re-trigger Greptile}

[mjstapp]

pushed fixes for some greptile comments...

[mjstapp]

@greptileai review