Merge #18638: net: Use mockable time for ping/pong, add tests

fa3365430c net: Use mockable time for ping/pong, add tests (MarcoFalke)
faab4aaf2f util: Add count_microseconds helper (MarcoFalke)

Pull request description:

  Switch `CNode::m_ping_start` and `CNetMessage::m_time` to mockable time, so that tests can be added.

  Mockable time is also type-safe, since it uses `std::chrono`

ACKs for top commit:
  jonatack:
    Code review re-ACK fa33654 re-read code, verified rebase per `git range-diff 4b5c919 fa94d6f fa33654`, previous tested ACKs still valid
  troygiorshev:
    ACK fa3365430c

Tree-SHA512: 7d632bd6019ce7c882029e71b667a61517e783af82755a85dd979ef09380934e172dec8b8f91d57b200a30a6e096aeaf01f19fee7f3aed0e0e871c72eb44d70e

test/functional/feature_maxuploadtarget.py

@@ -35,7 +35,11 @@ class MaxUploadTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
         self.num_nodes = 1
-        self.extra_args = [["-maxuploadtarget=800", "-acceptnonstdtxn=1"]]
+        self.extra_args = [[
+            "-maxuploadtarget=800",
+            "-acceptnonstdtxn=1",
+            "-peertimeout=9999",  # bump because mocktime might cause a disconnect otherwise
+        ]]
         self.supports_cli = False
 
         # Cache for utxos, as the listunspent may take a long time later in the test