v3.28.8: the batch panel's scroll preservation

The attempts box's content is replaced on every render (the batch panel is
static markup; the render fills the dynamic bits) and replacing a
scrollable element's content resets its scroll.  That was harmless while
the render ran once per attempt, but v3.28.7 made it run on every 2 s
poll, so scrolling back through the attempts during a run snapped to the
top each poll.

The render now captures the box's scrollTop before refilling it and
restores it afterwards.

Test: the stub box resets its scroll on an innerHTML write (like a
browser) and the render must keep the reader's position - verified to
fail without the restore.  920 frontend + 928 Python; sw cache
simple-v446.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pysim-simple-server"
-version = "3.28.7"
+version = "3.28.8"
 description = "HTTP REST server wrapping pysim for the SIMple PWA"
 requires-python = ">=3.8"
 # pysim is a git-only dependency installed explicitly by setup.bat/setup.sh.