frequency offset improvements

What this MR does / why we need it:

Initializes the ad5662 dac output to mid-scale which commands the VCTCXO to not skew the clock away from nominal.

Steps to complete before submitting MR:

• I have read Contribution guidelines

Release Notes

N/A

Changelog

enh(worker): initialize dac to mid-scale of output

Which issue(s) this MR closes

#58 (closed)