Restore HXCPP client tests #673
Description
Compiling the client to hxcpp with haxe 4.3 currently gives a broken program due to: HaxeFoundation/haxe#11666.
This meant I had to disable the cpp client tests in 50abb4e.
Resolving this requires either upgrading to the haxe 5 preview or waiting to see if another 4.3 bugfix is released.