PRF: only do expensive things once

Looking up MachAr was taking about 10ms which is way to slow to be
inside of the mouse motion event loop.

We are using it to get a constant so we can look it up and compute
the constant once at the top.

lib/matplotlib/transforms.py

@@ -50,7 +50,8 @@
 from .path import Path
 
 DEBUG = False
-
+# we need this later, but this is very expensive to set up
+MINFLOAT = np.MachAr(float).xmin
 MaskedArray = ma.MaskedArray
 
 
@@ -2738,7 +2739,7 @@ def nonsingular(vmin, vmax, expander=0.001, tiny=1e-15, increasing=True):
         swapped = True
 
     maxabsvalue = max(abs(vmin), abs(vmax))
-    if maxabsvalue < (1e6 / tiny) * np.MachAr(float).xmin:
+    if maxabsvalue < (1e6 / tiny) * MINFLOAT:
         vmin = -expander
         vmax = expander