Prefer staying inside regex to exiting it

[jakobnissen]

Currently, on Automa v1:

julia> compile(rep(onenter!(re"a+", :a)))
ERROR: Ambiguous NFA. After inputs "a", observing 'a' lead to conflicting action sets [:a] and nothing

Basically, Automa complains that the input aa can be interpreted as matching re"a+" once, or matching it twice. That's true, of course, but it's probably better if it's always interpreted as matching a single pattern. Maybe. I don't know.