v0.7.8 — fix proof-digest mismatch after restart from non-empty UTXO state

v0.7.8 — fix proof-digest mismatch after restart from non-empty UTXO state

BatchAVLProver::new snapshots tree.root into old_top_node. The resume
and snapshot-bootstrap branches constructed the prover around an empty
tree, then assigned the persisted root afterwards. old_top_node ended
up pointing at the sentinel infinity-leaf, so the first resumed block
produced a proof against an empty-tree baseline — permanent AD proofs
digest mismatch at stored_height+1.

Fixed by loading the root into the tree BEFORE constructing the prover,
so the constructor snapshots the canonical root.

Full Changelog: v0.7.7...v0.7.8