feat: Allow passing pointer arguments through mg.F

[fasmat]

With this change it is possible to use a target with flags / optional arguments in a mg.Deps or mg.SerialDeps definition through the use of mg.F:

func DependencyTarget(required string, optional *int) error {
   // ...
}

func MainTarget() error {
  var i = new(int)
  *i = 5
  mg.Deps(
    mg.F(DependencyTarget, "required", i)
  )

  // ...
}

or (since go 1.26)

func MainTarget() error {
  mg.Deps(
    mg.F(DependencyTarget, "required", new(5))
  )
  // ...
}