[unpackfs] Rework progress reporting

- Slice overall progress into chunks, with each chunk of equal size
  (as long as we have no overall count information) and place
  the progress of the current chunk into its own slice.

src/modules/unpackfs/main.py

@@ -269,19 +269,27 @@ class UnpackOperation:
         """
         progress = float(0)
 
-        done = 0
+        done = 0  # Done and total apply to the entry now-unpacking
         total = 0
-        complete = 0
+        complete = 0  # This many are already finished
         for entry in self.entries:
             if entry.total == 0:
+                # Total 0 hasn't counted yet
                 continue
-            total += entry.total
-            done += entry.copied
             if entry.total == entry.copied:
                 complete += 1
+            else:
+                # There is at most *one* entry in-progress
+                total = entry.total
+                done = entry.copied
+                break
 
         if done > 0 and total > 0:
-            progress = 0.05 + (0.90 * done / total) + (0.05 * complete / len(self.entries))
+            # Pretend that each entry represents an equal amount of work;
+            # the complete ones count as 100% of their own fraction
+            # (and have *not* been counted in total or done), while
+            # total/done represents the fraction of the current fraction.
+            progress = ( 1.0 * complete / len(self.entries) ) + ( ( 1.0 / len(self.entries) ) * done / total )
 
         job.setprogress(progress)