Add two extra saved cycles to PoS for denunciations checks

[Eitu33]

No further changes need to be done than saving 2 extra cycles because:

1. We feed every cycle we get after bootstrapping in compute_initial_draws
2. Fed cycles are computed in the same order they are fed and the selector thread checks sequentiality
3. We wait for every cycle to be drawn up to C+2 (C being the latest cycle received from bootstrap) here, and we now receive 6 cycles after this change, giving us the draws for C-2, C-1, C, C+1, C+2

[damip]

LGTM