Updated the guardian script to reach low noise in both 25W and 40W mode.

Attached is a DCPD cross-power spectrum at 40W (references) and at 25W (live data). Red is the PD_A-PD_B cross power. Blue is the DCPD_SUM power spectrum cast in the same units to give a reference of where shot noise lies.

Note: the excess noise we currently see is also present at 25W. It is almost identical to the 40W noise up to 200Hz. However, the notch structure between 200Hz and 700Hz is different at different power levels - no idea why.

Plot 2 shows the MICH coherence with DARM at 25W - the MICH-correction is not fine-tuned for that power level, but it is not the dominant contribution.

Guardian changes:
ISS_ON: based on IMC-PWR_IN_OUT16, set 25W or 40W offset.
        # crude way to make it work at 25W and 40W (no intermediate!)
        if ezca['IMC-PWR_IN_OUT16'] > 30:
            ezca['PSL-ISS_SECONDLOOP_REF_SIGNAL_ANA']= -0.9326934814453125  # 40W
        else:
            ezca['PSL-ISS_SECONDLOOP_REF_SIGNAL_ANA']= -0.588 # 25W
 

LOWNOISE_ASC: The state used to only run >35W. Changed it to always run, except for the 40W compensation filters on CHARD_Y and DHARD_Y (FM6).