In this PR, the Database interface in `core/state` has been extended
with one more function:
```go
// Iteratee returns a state iteratee associated with the specified state root,
// through which the account iterator and storage iterator can be created.
Iteratee(root common.Hash) (Iteratee, error)
```
With this additional abstraction layer, the implementation details can be hidden
behind the interface. For example, state traversal can now operate directly on
the flat state for Verkle or binary trees, which do not natively support traversal.
Moreover, state dumping will now prefer using the flat state iterator as
the primary option, offering better efficiency.
Edit: this PR also fixes a tiny issue in the state dump, marshalling the
next field in the correct way.
In order to reduce the amount of code that is embedded into the keeper
binary, I am removing all the verkle code that uses go-verkle and
go-ipa. This will be followed by further PRs that are more like stubs to
replace code when the keeper build is detected.
I'm keeping the binary tree of course. This means that you will still
see `isVerkle` variables all over the codebase, but they will be renamed
when code is touched (i.e. this is not an invitation for 30+ AI slop
PRs).
---------
Co-authored-by: Gary Rong <garyrong0905@gmail.com>
