The Azure Functions samples illustrate how to put the process entry point within a C# script file .csx. However, how can I achieve the behavior with a regular C# li
This is not currently supported, but you can publish your assembly with your function as described here and just have your function entry point call the appropriate method in your assembly:
#r "MyAssembly.dll"
public static void Run(/*...args...*/)
{
MyAssembly.MyMethod(/*..args...*/);
}