The Streamer with A=AlwaysMatchAutomaton does not need to maintain a stack of states

[fulmicoton]

This is an optimisation for the AlwaysMatchAutomaton

[fulmicoton]

We can probably improve the code with the poor man's specialization.

if automaton.always_match(state) {
   // ...
}

or even

if A::always_match() {
   // ...
}