This should lower the main thread's likelihood to immediately reacquire
cs_main after dropping it, which should help ThreadNotifyWallets and the
RPC methods to acquire cs_main more quickly.
Ported from ZEC commit e2cd1b761fe556bc6d61849346902c3611530307
Hush and DragonX do not have the same requirements for which nodes they
should talk to because they don't necessarily have consensus changes at
the same time. For instance, 3.10.0 was a consensus change for Hush but
not DragonX. This commit changes things so that Hush nodes will no
longer talk to old nodes that are not consensus compatible but leaves
things the same for DragonX mainnet, which has never had a consensus
change.
These NU's are always active for Hush Arrakis Chains so this code only serves
to slow down all operations by constantly being checked. So we disable them
which will speed up syncing, mining and creating transactions.
This is a greatly simplified and slightly tweaked version of
af2e3713e2
Their version will detect duplicate zkproofs across transactions while
this code will only detect duplicate zkproofs in a single ztx. If dupes
are found, the tx will be denied entry into the mempool.
This provides most of the benefit (increased CPU cost to attackers) with the
least code change and no annoyance to full node operators. Detecting
duplicate zkproofs across transactions requires a one-time reindex of
all of history, which means significant downtime for nodes.
Since Hush + HSCs have a much more strict policy on number of shielded
outputs and shielded inputs, only detecting duplicate zkproofs in
individual ztxs seems sufficient for now.
No correctly functioning node or wallet will ever create duplicate
zkproofs, so there is no worry of this accidentally affecting normal
users. Currently this is not a consensus rule but it could become one
in the future.
