castbar: pixel-snap progress via PixelUtil.SetStatusBarValue

Routes player and nameplate castbar progress through
PixelUtil.SetStatusBarValue so a 1.4s cast on a narrow bar no longer
shimmers across fractional pixels as it ticks. Adds GetMinMaxValues /
GetValue handlers to pfUI's custom StatusBar so PixelUtil can read the
current range.

modules/castbar.lua

@@ -237,7 +237,7 @@ pfUI:RegisterModule("castbar", function ()
         cur = cur > max and max or cur
         cur = cur < 0 and 0 or cur
 
-        this.bar:SetValue(cur)
+        PixelUtil.SetStatusBarValue(this.bar, cur)
 
         if this.showtimer then
           if this.delay and this.delay > 0 then

modules/nameplates.lua

@@ -1752,7 +1752,7 @@ end
         end
         barValue = barValue < 0 and 0 or barValue
         barValue = barValue > duration and duration or barValue
-        nameplate.castbar:SetValue(barValue)
+        PixelUtil.SetStatusBarValue(nameplate.castbar, barValue)
         SetCastbarText(nameplate.castbar, castInfo.endTime - now)
         if not nameplate.castbar.isShown then nameplate.castbar.isShown = true; nameplate.castbar:Show() end
       end
@@ -1787,7 +1787,7 @@ end
               nameplate.castbar.spell:SetText("")
             end
           end
-          nameplate.castbar:SetValue(cur)
+          PixelUtil.SetStatusBarValue(nameplate.castbar, cur)
           SetCastbarText(nameplate.castbar, channel and cur or (max - cur))
           if not nameplate.castbar.isShown then nameplate.castbar.isShown = true; nameplate.castbar:Show() end
         else