Rewrites triedb.GenerateTrie as a single partitioned pass that
reconciles stale account.Root fields and rebuilds the trie at the same
time, with 16-way parallelism and crash resume baked in.
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Co-authored-by: Gary Rong <garyrong0905@gmail.com>
This PR adds `GenerateTrie(db, scheme, root)` to the `triedb` package,
which rebuilds all tries from flat snapshot KV data. This is needed by
snap/2 sync so it can rebuild the trie after downloading the flat state.
The shared trie generation pipeline from `pathdb/verifier.go` was moved
into `triedb/internal/conversion.go` so both `GenerateTrie` and
`VerifyState` reuse the same code.
