fix(pdf): clear text layer before re-render to stop duplicated spans (v0.5.3)

TextLayer appends into the container without clearing it, so any
re-render of the same page doc (zoom settle, spread-scale update)
stacked a second span set at sub-pixel-shifted positions — selection
text reads doubled. Clear the container (stale spans + previous
endOfContent helper) before each TextLayer render.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "foliate-js",
-  "version": "0.5.2",
+  "version": "0.5.3",
   "description": "Render e-books in the browser",
   "repository": {
     "type": "git",