* Fix fringe case where the final `checkpoint()` must not be applied
why
If there are no `era` or `era1` files that can be imported from,
then the internal state will not be in sync with the DB state. This
would lead to overwriting the saved state block number with something
fancy. As a consequence the database becomes unusable for the next
process which will eventually fail with a state root mismatch.
* Update comment
* 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>