Use nanonext::.unresolved()

[wlandau]

From shikokuchuo/mirai#37, it will be much faster for crew than mirai::unresolved() when the task data is large.

[wlandau]

This means I can remove the n argument from collect() with no loss of efficiency!

[wlandau]

Thinking about how to manage this back-compatibly. Maybe I want to grab the function only if it exists in nanonext:

if (exists(x = ".unresolved", envir = getNamespace(name = "nanonext"))) {
  mirai_unresolved <- eval(expr = parse(text = "nanonext::.unresolved"))
} else {
  mirai_unresolved <- nanonext::unresolved
}

The eval(parse()) is to hide from the R CMD check static code analyzer.

[wlandau]

Then when the next nanonext is released, I can revert this workaround and require that version of nanonext.

[wlandau]

5c046c9 moves entirely to .unresolved() and requires the recently released version 0.8.1 of nanonext.