profiler: min-length content compare on size/record mismatch

When a declared fileSize/recordLen/numRecords attribute mismatches, compare
file contents only over the overlapping (shorter) portion, so a length
difference alone doesn't fail the content check when the common bytes match.
When sizes match, contents are compared fully as before.

Add profilerMatchMin helper + tests. SW cache v43.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'otaman-v42';
+const CACHE = 'otaman-v43';
 const URLS = [
   'index.html',
   'help.html',