Speed up arrayToQPath when connect='pairs'

As discussed earlier, the process of QDataStream >> QPainterPath is
quite slow, so this commit makes an improvement on QPainterPath creation
for the case of connect='pairs' by using a naive method of moving the
path and drawing a line on the path.  This was the fastest method
identified during testing.

pyqtgraph/functions.py

@@ -14,8 +14,11 @@ import struct
 import sys
 import warnings
 import math
+import functools
+import itertools
 
 import numpy as np
+from numpy.lib import recfunctions as rfn
 from .util.cupy_helper import getCupy
 from .util.numba_helper import getNumbaFunctions
 
@@ -1759,8 +1762,18 @@ def arrayToQPath(x, y, connect='all', finiteCheck=True):
         path.addPolygon(polygon)
         return path
     elif eq(connect, 'pairs'):
-        arr[:]['c'][::2] = 0
-        arr[:]['c'][1::2] = 1  # connect every 2nd point to every 1st one
+        xs = arr['x'].tolist()
+        ys = arr['y'].tolist()
+ 
+        lineTo = path.lineTo
+        moveTo = path.moveTo
+        for elementType, x, y in zip(
+            itertools.cycle((moveTo, lineTo)),
+            xs,
+            ys
+        ):
+            elementType(x, y)
+        return path
     elif eq(connect, 'finite'):
         # Let's call a point with either x or y being nan is an invalid point.
         # A point will anyway not connect to an invalid point regardless of the