Handle variable renaming in Petri net semantics

Variables which names start with an underscore lead to an error in the debugger[1] and in the memory model analysis[2]. The bug can be triggered with the following code:

mainAgent {
    int _007;
}

1: The debugger could not be initialized. Failed to parse "{ context, vars: { ...vars, _007: 0 } }" as expression: Expected expression but "{" found.

2: Expected "}" (at char 16), (line:2, col:5)