* Rename WakuMode to LogosDeliveryMode, add Fleet mode
* KernelConf (which starts only kernel) is now a distinct WakuNodeConf (starts messaging, for tests)
* Add LogosDelivery.new(kernelConf) (kernel-only)
* Add LogosDelivery.new(kernelConf, messagingOverrides, channelsOverrides) (full stack)
* LogosDeliveryConf.messagingOverrides/channelsOverrides are Option and mount each layer if present
* Add kernel-only LogosDeliveryConf.init(kernelConf)
* Parse {"mode": "fleet", "kernelConf": {...}} in parseLogosDeliveryConf
* Generalize parseOverrides to parse over caller-supplied defaults
* Add requireMessaging/requireChannels FFI guards and apply them
* Make start/stop skip layers that were not mounted (no config)
* Rename toKernelConf to toWakuNodeConf
* Add tests to test_conf.nim
* Misc additions/refactors
* Move waku.nim from waku/factory to under waku/
* remove unused
* Realize Kernel API in scope of Waku class
* Refactor waku/api into messaging_client, waku/api/types and api_conf into logos_delivery/api
* Make liblogosdelivery and wakunode2 compile, remove waku/api.nim as it was just a import orchestrator
* make test compile and run
* Reconcile master's new send tests to LogosDelivery API after rebase
master commits #3965/#3669-followup added two test cases (Edge lightpush
delivery #3847, store-validation timeout) written against the removed
waku/api.nim createNode helper. Rewrite them to the LogosDelivery shape:
createNode -> LogosDelivery.new, node.node -> node.waku.node,
node.brokerCtx -> node.waku.brokerCtx, node.send -> node.messagingClient.send,
and drop the now-implicit mountMessagingClient calls (LogosDelivery.new
mounts the client internally).
