ZMQ get_output_distribution duplicate amount DoS

Summary

ZMQ get_output_distribution RPC is vulnerable to memory exhaustion DoS.

The method accepts an unbounded amounts array and returns a separate distribution for each entry. Repeating amount 0 causes the daemon to duplicate the full RingCT output distribution many times, allowing a small request to expand into a very large response.

The issue is also reachable with --restricted-zmq-rpc, because ZMQ lacks the stricter validation applied by restricted HTTP RPC.

Resolved in https://github.com/monero-project/monero/pull/10419 and v0.18.5.0.