Remove redundant/impure `StatsObj` `Fn0` methods

[pete-murphy]

Each of these methods

purescript-node-fs/src/Node/FS/Stats.purs

Lines 35 to 40 in a9da8b9

	, isFile :: Fn0 Boolean
	, isDirectory :: Fn0 Boolean
	, isBlockDevice :: Fn0 Boolean
	, isCharacterDevice :: Fn0 Boolean
	, isFIFO :: Fn0 Boolean
	, isSocket :: Fn0 Boolean

has a corresponding standalone Stats -> Boolean function so they seem redundant, and using the isDirectory :: Fn0 Boolean directly resulted in this issue aristanetworks/purescript-backend-optimizer#35 because this context wasn't preserved after compilation.

[pete-murphy]

A minimal example that produces runtime error (without going through purs-backend-es)

module Main where

import Prelude

import Data.Function.Uncurried (runFn0)
import Effect (Effect)
import Effect.Class.Console (log)
import Node.FS.Stats (Stats(..))
import Node.FS.Sync (stat)

main :: Effect Unit
main = do
  isDir <- runFn0 <<< (case _ of Stats statsObj -> statsObj.isDirectory) <$> stat "."
  if isDir then
    log "Directory"
  else log "Not directory"

fails with

❯ spago run
[info] Build succeeded.
node:internal/fs/utils:416
  return this._checkModeProperty(S_IFDIR);
              ^

TypeError: Cannot read properties of undefined (reading '_checkModeProperty')
    at StatsBase.isDirectory (node:internal/fs/utils:416:15)