Node crash via duplicate shielded transaction

Denial of service in Zcash Foundation Zebra before 4.5.0 allows remote attackers to crash the node via duplicate shielded transactions in parent and child blocks. In zebra-state/src/service/non_finalized_state/chain.rs, Chain::push inserts the transaction hash into tx_loc_by_hash and asserts uniqueness before it updates shielded state and runs the duplicate Sprout, Sapling, or Orchard nullifier checks. Exploitation requires non-finalized NU5-or-later block processing and either two attacker-mined consecutive blocks or one attacker-mined child after an honest parent includes the attacker's shielded transaction; release builds abort the entire zebrad process instead of cleanly rejecting the child block.