Improve consistency of colorsys.rgb_to_hsv (GH-27277)

Cache repeated difference to make code easier to read and consistent with colorsys.rgb_to_hls.

Lib/colorsys.py

@@ -125,13 +125,14 @@ def _v(m1, m2, hue):
 def rgb_to_hsv(r, g, b):
     maxc = max(r, g, b)
     minc = min(r, g, b)
+    rangec = (maxc-minc)
     v = maxc
     if minc == maxc:
         return 0.0, 0.0, v
-    s = (maxc-minc) / maxc
-    rc = (maxc-r) / (maxc-minc)
-    gc = (maxc-g) / (maxc-minc)
-    bc = (maxc-b) / (maxc-minc)
+    s = rangec / maxc
+    rc = (maxc-r) / rangec
+    gc = (maxc-g) / rangec
+    bc = (maxc-b) / rangec
     if r == maxc:
         h = bc-gc
     elif g == maxc: