* Tighten `CoreDb` API for accounts
why:
Apart from cruft, the way to fetch the accounts state root via a
`CoreDbColRef` record was unnecessarily complicated.
* Extend `CoreDb` API for accounts to cover storage tries
why:
In future, this will make the notion of column objects obsolete. Storage
trees will then be indexed by the account address rather than the vertex
ID equivalent like a `CoreDbColRef`.
* Apply new/extended accounts API to ledger and tests
details:
This makes the `distinct_ledger` module obsolete
* Remove column object constructors
why:
They were needed as an abstraction of MPT sub-trees including storage
trees. Now, storage trees are handled by the account (e.g. via address)
they belong to and all other trees can be identified by a constant well
known vertex ID. So there is no need for column objects anymore.
Still there are some left-over column object methods wnich will be
removed next.
* Remove `serialise()` and `PayloadRef` from default Aristo API
why:
Not needed. `PayloadRef` was used for unstructured/unknown payload
formats (account or blob) and `serialise()` was used for decodng
`PayloadRef`. Now it is known in advance what the payload looks
like.
* Added query function `hasStorageData()` whether a storage area exists
why:
Useful for supporting `slotStateEmpty()` of the `CoreDb` API
* In the `Ledger` replace `storage.stateEmpty()` by `slotStateEmpty()`
* On Aristo, hide the storage root/vertex ID in the `PayloadRef`
why:
The storage vertex ID is fully controlled by Aristo while the
`AristoAccount` object is controlled by the application. With the
storage root part of the `AristoAccount` object, there was a useless
administrative burden to keep that storage root field up to date.
* Remove cruft, update comments etc.
* Update changed MPT access paradigms
why:
Fixes verified proxy tests
* Fluffy cosmetics
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