Setting seed in cvfit should not affect global seed

[pbreheny]

This line in L0Learn.cvfit() introduces unintended side effects:

L0Learn/R/cvfit.R

Line 40 in fdfe13b

set.seed(seed)

In particular, it affects the RNG seed in the global environment so that if, say, someone is carrying out a simulation and calls L0Learn.cvfit(), it can throw off the whole simulation.

Better to do something like this:

original_seed <- .GlobalEnv$.Random.seed
on.exit(.GlobalEnv$.Random.seed <- original_seed)
set.seed(seed)