When sampling from normal distribution in Sink, warn when efficiency is low

[nuclearkatie]

Sink can call the PRNG to determine the size of material to request, from 0 to the maximum allowable (throttled by the throughput or total capacity). When using a normal distribution, the mean and standard deviation of those requests are only limited to positive values.

However, this could result in very inefficient calls to the PRNG, resulting in significant numbers of rejected samples.

Could create a warning when the user has chosen an inefficient $\mu$ and $\sigma$