* 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
* deep changes in libwaku to adap to nim-ffi
* start using ffi pragma in library
* update some binding examples
* add missing declare_lib.nim file
* properly rename api files in library folder
