* Handle last/all node(s) proof conditions at leaf node extractor
detail:
Flag whether the maximum extracted node is the last one in database
No proof needed if the full tree was extracted
* Clean up some helpers & definitions
details:
Move entities to more plausible locations, e.g. `Account` object need
not be dealt with in the range extractor as it applies to any kind of
leaf data.
* Fix next/prev database walk fringe condition
details:
First check needed might be for a leaf node which was done too late.
* Homogenise snap/1 protocol function prototypes
why:
The range arguments `origin` and `limit` data types differed in various
function prototypes (`Hash256` vs. `openArray[byte]`.)
* Implement `GetStorageRange` handler
* Implement server timeout for leaf node retrieval
why:
This feature leaves control on the server for probably costly action
invoked by the network
* Implement maximal reply size for snap service
why:
This feature leaves control on the server for probably costly action
invoked by the network.