Zabbix

........S. [ZBX-27453] fixed average trend calculation to avoid producing inf values when dealing with DBL_MAX input; updated timeleft() function to return DBL_MAX when threshold cannot be reached and history approaches DBL_MAX

Merge in ZBX/zabbix from feature/ZBX-27453-7.4 to release/7.4

* commit 'a20c2f4662cc0db15c900003af37725266e8e863':
  ........S. [ZBX-27453] added one more minor comment fix to integration test
  ........S. [ZBX-27453] added minor comment fixes to integration test
  ........S. [ZBX-27453] added back wrongly removed test line
  ........S. [ZBX-27453] removed test with ns precision and also updated Changelog
  ........S. [ZBX-27453] added comments to tests that are different from 7.5
  ........S. [ZBX-27453] added test to directly cover the scenario where val_now below threshold and slope rising (issue B)
  ........S. [ZBX-27453] updated test to match the 7.4 behaviour when threshold gets instantly reached
  ........S. [ZBX-27453] updated tests to confirm NaNs
  ........S. [ZBX-27453] added tests from proposed patch for master branch
  ........S. [ZBX-27453] updated trend_avg() function to avoid producing inf values when dealing with DBL_MAX input