This answer could be totally wrong. It just describes the shades of meaning that the terms have for me.
To me, "number sense" feels more specific and has the connotation of describing someone who habitually and competently makes sense out of numerical relationships. For example, I teach my students to do order-of-magnitude estimates (Fermi problems), and once I posed a problem of estimating the amount of blood sucked by a flea. One of my students estimated a liter. This student lacked number sense. He wasn't in the habit of thinking about whether numbers made sense, and/or he wasn't competent enough to tell that this particular number didn't make sense.
Another example of lacking number sense is when someone writes the result of an experiment as $0.03798\pm 0.00213$, not understanding that it doesn't make sense to express the result to the 100,000ths place when the uncertainty is in the thousandths place.
"Numeracy" feels to me more like a broad term that describes facility with numbers. For example, someone who is numerate should understand that a hamburger with a 1/3 pound patty contains more meat than one with a 1/4 pound patty. (There was a famous ill-fated advertising campaign that didn't anticipate how many people figured 1/4 pound to be more meat, since 4 is greater than 3.)
A numerate person can estimate, without reaching for a calculator, that \$12 is about 1% of \$1000.
A numerate person may not have memorized what 7x6 is, but if necessary they can reconstruct it in a few seconds by doing (7x3)x2. If someone lacks numeracy, then not only do they not have 7x6=42 memorized, but they can't reconstruct that fact.