Add handling of functions for Unity method invocations

[Danand]

Changes

• Add MessageReceived public event for handling simple calls with single string argument
• Add HandleInvocation() private utility method for handling calls with custom arguments

Example

Here is example usage of UnityPoco.invoke()

Poco-side

poco = UnityPoco()
poco.invoke(listener="say_hello", name="anonymous", year=2024)

Unity-side

1. Derive some new class from PocoListenerBase

2. Add method:

   [PocoMethod("say_hello")]
   public void SayHello(string name, int year)
   {
       Debug.Log("Hi, ${name}! {year} is coming soon!");
   }

3. Add reference at PocoManager to ancestor of PocoListenerBase

Dependencies

Depends on AirtestProject/Poco#607