[hf] sc: bump kotlin to next minor version (1.5.10)

• sc: bump kotlin to next minor version (1.4.30 -> 1.5.10)
• bump libs with direct dependency on this as well (and our test libs b/c why not?)
• follow deprecation warnings to remove deprecated helpers of form 4.seconds and replace with functions of form Duration.milliseconds(4) (sigh! liked the old one!)
  • side-effect: Intellij's auto-fix feature for replacing deprecated functions also did a bunch of code cleanup that inserted random white-space throughout the files that it touched
• fix flakey unsubscribe tests (by inserting eventually blocks)