net, rpc: expose nLastBlockTime/nLastTXTime as last block/last_transaction in getpeerinfo
Summary:
This PR adds inbound peer eviction criteria nLastBlockTime and nLastTXTime to CNodeStats and CNode::copyStats, which then allows exposing them in the next commit as last_transaction and last_block Unix Epoch Time fields in RPC getpeerinfo.
Backport of core#19731.
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D9331