obsdiscovery: extract a smarted depth in utility The function is reusing previous depth for ancestors unless this is a merge.

obsdiscovery: simply some of the missing computation

discovery: implement some range based discovery This use the previously implemented methods to implement some discovery and fetch method using ranges. There is currently major performance issue and some aspect of the protocol will changes.

discovery: introduce a official 'obshash associated to a range The hash in a combination of the hash a its subrange. If the range is a leaf, we have the obsmarker relevant to the node in that leaf range.