add package init functions when algo is rta

[cnzhujie]

Package init method is missed under rta algo. For example:

main.go

package main

func main() {
    method() 
}

func init() {
    method()    
}

func method() {
}

go.mod

module example.com/graph/example_init

go 1.20

go-callvis -algo rta example.com/graph/example_init

[ondrajz]

Thank you.