libzipplugin: replace almost all raw pointers with unique_ptr

What title says.

Lines 76 and 401 are still cause memory leaks when you working with same ark instance, like reopening big files (qt sources archive for example), or move (copy/paste) internal files inside opened zip file.

our_unique_ptr i found usefull as it reduces unique_ptr memory size for declaring custom destructor for that unique_ptr.