Also enables only spawning the mdns service when debug in the coordinator.

Prior undetected due to relase builds not having bounds checks enabled.

…n debug mode

This is *probably* worth an issue filed upstream, if it can be tracked down.

These debug asserts assumed there was a change address to take the remainder.
If there's no change address, the remainder is shunted to the fee, causing the
fee to be distinct from the estimate.

We presumably need to modify monero-serai such that change: None isn't valid,
and users must use Change::Fingerprintable(None).