* Simplify txFrame protocol, improve persist performance
To prepare forked-layers for further surgery to avoid the nesting tax,
the commit/rollback style of interacting must first be adjusted, since
it does not provide a point in time where the frame is "done" and goes
from being actively written to, to simply waiting to be persisted or
discarded.
A collateral benefit of this change is that the scheme removes some
complexity from the process by moving the "last saved block number" into
txframe along with the actual state changes thus reducing the risk that
they go "out of sync" and removing the "commit" consolidation
responsibility from ForkedChain.
* commit/rollback become checkpoint/dispose - since these are pure
in-memory constructs, there's less error handling and there's no real
"rollback" involved - dispose better implies that the instance cannot be
used and we can more aggressively clear the memory it uses
* simplified block number handling that moves to become part of txFrame
just like the data that the block number references
* avoid reparenting step by replacing the base instead of keeping a
singleton instance
* persist builds the set of changes from the bottom which helps avoid
moving changes in the top layers through each ancestor level of the
frame stack
* when using an in-memory database in tests, allow the instance to be
passed around to enable testing persist and reload logic
By introducing the "shared rocksdb instance" concept to the backend, we
can remove the "piggybacking" mode , thus reducing the complexity of
database initialisation and opening the possibility of extending how
write batching works across kvt/aristo.
The change makes explicit the hidden shared state that was previously
hiding in closures and provides the first step towards simplifying the
"commit/persist" interface of coredb, preparing it for optimizations to
reduce the "layering tax" that `forked-layers` introduced.
* renamed nimbus folder to execution_chain
* Renamed "nimbus" references to "execution_chain"
* fixed wrongly changed http reference
* delete snap types file given that it was deleted before this PR merge
* missing 'execution_chain' replacement
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Co-authored-by: pmmiranda <pedro.miranda@nimbus.team>
