optimize sampler to apply demuxing at symbols rate

tests/test_sampling.py

@@ -4,8 +4,8 @@ import numpy as np
 
 def test_resample():
     x = np.arange(300)
-    s = sampling.Sampler(x)
-    y = np.array(list(s))
+    s = sampling.Sampler(x, interp=sampling.Interpolator())
+    y = s.take(len(x) - s.interp.width - 1)
 
     err = x[1:len(y)+1] - y
     assert np.max(np.abs(err)) < 1e-10