External receivers should be enabled for single contract file compilation

[anton-trunov]

If externals are not used there will be no FunC output differences, so to make local debugging and testing easier it would be enable external option in the config that we create on-the-fly

[novusnota]

You'll only need to add external: true in options there and it should be done

https://github.com/tact-lang/tact/blob/e2f5eabcd7e6027e36755b858b152f2716f30cb7/src/node.ts#L26