core, eth, trie: filter out boundary nodes and remove dangling nodes in stacktrie (#28327)
* core, eth, trie: filter out boundary nodes in stacktrie
* eth/protocol/snap: add comments
* Update trie/stacktrie.go
Co-authored-by: Martin Holst Swende <martin@swende.se>
* eth, trie: remove onBoundary callback
* eth/protocols/snap: keep complete boundary nodes
* eth/protocols/snap: skip healing if the storage trie is already complete
* eth, trie: add more metrics
* eth, trie: address comment
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Co-authored-by: Martin Holst Swende <martin@swende.se>