This changes some of the remaining time variable in net_processing.cpp from int64_t to std::chrono. The PR description claims to change all the remaining variables in net_processing, but more are done in follow-up PR 23832
This is a backport of core#23801
It also includes commit https://github.com/bitcoin/bitcoin/pull/21562/commits/a28bfd1d4cfa523a6abf3832dbfd6183cd546944