feat: let cwdHook be configurable

[antongolub]

process.cwd() // foo
$.cwdHook = false

within(async() => {
   cd('/bar')
   await sleep(10)
   await $`pwd` // now it is `/qux`, not `/bar`
})

cd('/qux')

relates #589

[antonmedv]

Let's rename to $.syncProcessCwd?

[antongolub]

$.cwdSyncHook ?
to provide more symmetry with $.cwd