utcfromtimestamp was deprecated and nobody told me,

not even the deprecationwarning that got silently generated burning
20~30% of all CPU-time without actually displaying it anywhere, nice

python 3.12.0 is now only 5% slower than 3.11.6

also fixes some other, less-performance-fatal deprecations

scripts/sfx.py

@@ -295,7 +295,10 @@ def unpack():
         # the only possible input is a single tar.bz2
         # which gets hardcoded into this script at build stage
         # skip 0
-        tf.extractall(mine)
+        try:
+            tf.extractall(mine, filter="tar")
+        except TypeError:
+            tf.extractall(mine)
 
     os.remove(tar)