Merge #21015: Make all of net_processing (and some of net) use std::chrono types

0eaea66e8b Make tx relay data structure use std::chrono types (Pieter Wuille)
55e82881a1 Make all Poisson delays use std::chrono types (Pieter Wuille)
c733ac4d8a Convert block/header sync timeouts to std::chrono types (Pieter Wuille)
4d98b401fb Change all ping times to std::chrono types (Pieter Wuille)

Pull request description:

  (Picking up #20044. Rebased against master.)

  This changes various uses of integers to represent timestamps and durations to `std::chrono` duration types with type-safe conversions, getting rid of various `.count()`, constructors, and conversion factors.

ACKs for top commit:
  jnewbery:
    utACK 0eaea66e8b
  vasild:
    ACK 0eaea66e8b
  MarcoFalke:
    re-ACK 0eaea66e8b, only changes: minor rename, using C++11 member initializer, using 2min chrono literal, rebase 🤚
  ajtowns:
    utACK 0eaea66e8b

Tree-SHA512: 2dbd8d53bf82e98f9b4611e61dc14c448e8957d1a02575b837fadfd59f80e98614d0ccf890fc351f960ade76a6fb8051b282e252e81675a8ee753dba8b1d7f57

src/net_processing.h

@@ -29,7 +29,7 @@ struct CNodeStateStats {
     int nSyncHeight = -1;
     int nCommonHeight = -1;
     int m_starting_height = -1;
-    int64_t m_ping_wait_usec;
+    std::chrono::microseconds m_ping_wait;
     std::vector<int> vHeightInFlight;
 };