My company recently purchased the Full-Calendar Scheduler addon. Is there a proper way to hide the license key in code? What are good practices for this?
You're right, there's no way to completely hide the schedulerLicenseKey from someone malicious wanting to steal it, however, a thief could much more easily use the universal GPL license key if they wanted a warning-free version of Scheduler, so it's a moot point.
In essence, the actual characters of the license key are not that secret. The license key is mainly used to know when to prompt the developer that they have upgraded past their allowed version upgrade window. Beyond this, it is essentially an honor system. This is why not much attempt is made to encrypt/validate the key.