Animancer Lite does not include its source code (it has some parts but not the main core of the system as explained in the Feature Comparison). Instead, it is distributed as a pair of DLL files; one for the Unity Editor to use and another to be used in runtime builds. Their import settings are as follows:

Editor DLL Runtime DLL
Assets/Plugins/Animancer/Internal/Core/Animancer.Lite.dll Assets/Plugins/Animancer/Internal/Animancer.Lite.dll
Editor only All platforms except Editor

Animancer Pro includes its full source code. It also contains DLLs in those same locations, but they are only empty dummies to overwrite the ones from the Lite version when you upgrade to Pro. They contain no code and are not included in runtime builds.