[CRe] Tweak nightmode and CRe call cache interaction (#6859)

Simplify 4caf8f28 (#6854), allowing us not to track
nightmode in two places.

frontend/document/credocument.lua

@@ -25,7 +25,6 @@ local CreDocument = Document:new{
     _view_mode = nil,
     _smooth_scaling = false,
     _nightmode_images = true,
-    _nightmode = false,
 
     line_space_percent = 100,
     default_font = "Noto Serif",
@@ -424,7 +423,7 @@ function CreDocument:drawCurrentView(target, x, y, rect, pos)
 
     --local start_ts = FFIUtil.getTimestamp()
     self._drawn_images_count, self._drawn_images_surface_ratio =
-        self._document:drawCurrentPage(self.buffer, self.render_color, self._nightmode and self._nightmode_images, self._smooth_scaling, Screen.sw_dithering)
+        self._document:drawCurrentPage(self.buffer, self.render_color, Screen.night_mode and self._nightmode_images, self._smooth_scaling, Screen.sw_dithering)
     --local end_ts = FFIUtil.getTimestamp()
     --print(string.format("CreDocument:drawCurrentView: Rendering took %9.3f ms", (end_ts - start_ts) * 1000))
 
@@ -878,11 +877,6 @@ function CreDocument:setNightmodeImages(toggle)
     self._nightmode_images = toggle
 end
 
-function CreDocument:setNightMode(toggle)
-    logger.dbg("CreDocument: set nightmode", toggle)
-    self._nightmode = toggle
-end
-
 function CreDocument:setFloatingPunctuation(enabled)
     --- @fixme occasional segmentation fault when toggling floating punctuation
     logger.dbg("CreDocument: set floating punctuation", enabled)
@@ -1055,6 +1049,9 @@ function CreDocument:register(registry)
     registry:addProvider("py", "text/x-python", self, 90)
 end
 
+-- no-op that will be wrapped by setupCallCache
+function CreDocument:resetCallCache() end
+
 -- Optimise usage of some of the above methods by caching their results,
 -- either globally, or per page/pos for those whose result may depend on
 -- current page number or y-position.
@@ -1274,6 +1271,7 @@ function CreDocument:setupCallCache()
             elseif name:sub(1,6) == "update" then add_reset = true
             elseif name:sub(1,6) == "enable" then add_reset = true
             elseif name == "zoomFont" then add_reset = true -- not used by koreader
+            elseif name == "resetCallCache" then add_reset = true
 
             -- These may have crengine do native highlight or unhighlight
             -- (we could keep the original buffer and use a scratch buffer while