I have never charged my clients for lunch-time or breaks, and I have never paid a subcontractor for it before either (at least not to my knowledge).
My view has always been that subcontracting has many positives (higher pay, autonomy, etc.) and many negatives (no benefits, etc.) and one of the negatives is you get paid for productive time, which does not include lunch or breaks.
But I still wonder, should subcontractors be paid like employees, for lunch breaks, coffee breaks etc.?