Can someone take your source code from an iOS build file?

So say for example you are making an iOS game (or android) for a client, they have bought or licensed a game for you to develop for them but the source code is yours. You will gladly give them the finished game when it is done but you don't want them to have the source code and you only agreed to deliver the finished build not the actual unity file.

So when you build the game for iOS it comes with a rather large file of folders inside folders and large amounts of individual files inside those folders; Say you deliver this file to the client rather than uploading it yourself to their app store, can they use the build file you delivered to them to take the source code(your scripts, your assets, etc.)? And same thing goes for Android Builds - can they take your source code from your .apk build file?

Bottom line is can they use the iOS build file you made to get your source code? Or is it better to just straight up upload the build file to their app store yourself?