test_compose asserts the new decnet.topology.* labels land on both base
deckies (role=base, no service marker) and service fragments
(service=true). The stub docker client in test_deploy grew a filters
kwarg so it keeps matching the real .networks.list(filters=...) call
signature now used by the deployer.
Adds per-topology compose generation (one Docker bridge network per
LAN, multi-homed bridge deckies, ip_forward sysctl for L3 forwarders)
plus async deploy_topology/teardown_topology in the engine. Leaf-first
teardown via BFS-named LAN reverse sort; partial-state safe on failure.
