feat: add support for conditional packet attribute

feat: add checking parameter method for the generator

feat: add packet greedy attribute

feat: add support for optional parameters

fix: correct generated syntax errors

feat: rewrite packet serializer generator

feat: skip to last token of nested levels if possible

fix: generate serializers for nullable types correctly

fix: syntax errors in list attribute generator

feat: add base packet list source generators

fix: handle non-nullable values correctly in packet index code generator

feat: add source generator for basic packet converter