* Rename `LeafRange` => `NodeTagRange`
* Replacing storage slot partition point by interval
why:
The partition point only allows to describe slots `[point,high(Uint256)]`
for fetching interval slot ranges. This has been generalised for any
interval.
* Replacing `SnapAccountRanges` by `SnapTrieRangeBatch`
why:
Generalised healing status for accounts, and later for storage slots.
* Improve accounts healing loop
* Split `snap_db` into accounts and storage modules
why:
It is cleaner to have separate session descriptors for accounts and
storage slots (based on a common base descriptor.)
Also, persistent storage handling might be changed in future which
requires the storage slot implementation disentangled from the accounts
handling.
* Re-model worker queues for storage slots
why:
There is a dynamic list of storage sub-tries, each one has to be
treated similar to the accounts database. This applied to slot
interval downloads as well as to healing
* Compress some return value report lists for snapdb methods
why:
No need to report all handling details for work items that are filteres
out and discarded, anyway.
* Remove inner loop frame from healing function
why:
The healing function runs as a loop body already.
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