Rust-language assets for Zcash
`queue_tx_retrieval` cannot re-request a transaction whose stored `raw` does not parse
zcash_primitives: add PHGR proof, ephemeralKey, encCiphertexts, getters to JsDescription
rewindToHeight affects spendability
zcash_client_backend: surface a reorg deeper than the wallet's rewind window as a distinct condition requiring intervention
zcash_client_backend: Use knowledge of inserted treestates to reduce time to spendability