* core/state/snapshot: check dangling storages when generating snapshot

* core/state/snapshot: polish

* core/state/snapshot: wipe the last part of the dangling storages

* core/state/snapshot: fix and add tests

* core/state/snapshot: fix comment

* README: remove mentions of fast sync (#24656)
Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>

* core, cmd: expose dangling storage detector for wider usage

* core/state/snapshot: rename variable

* core, ethdb: use global iterators for snapshot generation

* core/state/snapshot: polish

* cmd, core/state/snapshot: polish

* core/state/snapshot: polish

* Update core/state/snapshot/generate.go
Co-authored-by: Martin Holst Swende <martin@swende.se>

* ethdb: extend db test suite and fix memorydb iterator

* ethdb/dbtest: rollback changes

* ethdb/memorydb: simplify iteration

* core/state/snapshot: update dangling counter

* core/state/snapshot: release iterators

* core/state/snapshot: update metrics

* core/state/snapshot: update time metrics

* metrics/influxdb: temp solution to present counter meaningfully, remove it

* add debug log, revert later

* core/state/snapshot: fix iterator panic

* all: customized snapshot iterator for backward iteration

* core, ethdb: polish

* core/state/snapshot: remove debug log

* core/state/snapshot: address comments from peter

* core/state/snapshot: reopen the iterator at the next position

* ethdb, core/state/snapshot: address comment from peter

* core/state/snapshot: reopen exhausted iterators
Co-authored-by: Tbnoapi <63448616+nuoomnoy02@users.noreply.github.com>
Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>
Co-authored-by: Martin Holst Swende <martin@swende.se>