Bound GetAddressUtxos result materialization

[Zk-nd3r]

Summary

Fixes #974 by threading the start_height and max_entries request bounds into the internal GetAddressUtxos path instead of materializing the full converted result first.

What changed

• Added an internal AddressUtxosRequest carrying addresses, start_height, and optional max_entries.
• Added ChainIndex::get_address_utxos_bounded(...) while preserving the existing unbounded get_address_utxos(...) behavior.
• Wired fetch/state lightwallet unary and stream handlers through the bounded chain-index path.
• Applied bounds while converting state-backed UTXO rows, so the converted Vec<GetAddressUtxos> stops at the requested limit.
• Applied bounds after the unavoidable validator RPC response on the fetch path; the upstream getaddressutxos RPC has no height/limit parameters.
• Extended the mockchain test to cover default unbounded behavior, explicit None bounds, max_entries=Some(1), and start_height filtering.

Validation

Ran against current zingolabs:dev (c4d8f381):

• rustfmt --edition 2021 --check on the 8 changed files
• git diff --cached --check
• Amsterdam Linux: cargo check -p zaino-state -p zaino-fetch
• Amsterdam Linux: cargo test -p zaino-state get_address_utxos -- --nocapture
  • 1 passed; 0 failed; 139 filtered out