the (an?) editor exported those files to generate your app (?) in which case you’d run the player to launch your app.
you expect the engine to provide IO functionality for those formats. in which case you must know that these might not be a standard or something common like a .zip file.
you want to implement your own custom package file. in which case the engine does not allow such thing by default. you’d have to break outside the engine scope and make a few modifications to the engine itself.
Where did these package files come from? The file extension .espak leads me to believe it is some sort of package file for a different engine or game. Knowing where the thing came from, and what engine it was built for, would certainly help in determining if and how it could be converted to be used with Urho3D.