Add Trie.Walk() for exhaustive traversal that resolves expired nodes
with hash verification. Add `archive verify` subcommand that walks
the full state (account + storage tries) to validate all archived
data can be correctly resurrected.
Delete both the journal KV entry and file after archiving to force
geth to restart with a bare disk layer, rewinding the chain head to
the persistent disk state and re-executing blocks.
Also adds markSubtreeDirty() to resolveExpiredNodeData() so that all
nodes in a resolved expired subtree are captured in the NodeSet during
commit — preventing them from being lost between diff layers and the
raw DB.
