makeClusterPSOCK(): Protect against creating too many local workers

[HenrikBengtsson]

(This was triggered by https://stackoverflow.com/questions/77244972)

There's nothing that prevents us from doing:

cl <- makeClusterPSOCK(n)

where n is very large, e.g. n = 1000.

To protect against this, makeClusterPSOCK() could compare n > availableCores() and:

• produce an informative warning, or
• produce an informative error

If an error, then there should be an option to override it, e.g. force = TRUE. Of course, one can always workaround it by merging many smaller clusters, e.g.

cl <- c(makeClusterPSOCK(8), makeClusterPSOCK(8))

[HenrikBengtsson]

Implemented and now documented in ?makeClusterPSOCK (https://parallelly.futureverse.org/reference/makeClusterPSOCK.html).