use tuple up front instead of list which must later be converted to tuple

We don't need a mutable type, anyway, and the only other use of it is
recreating the list as = tuple(map(...)) so why convert *again* to a
tuple?

src/calibre/utils/fonts/sfnt/subset.py

@@ -266,7 +266,7 @@ def main(args):
 
     for c in chars:
         if '-' in c:
-            parts = [x.strip() for x in c.split('-')]
+            parts = tuple(x.strip() for x in c.split('-'))
             if len(parts) != 2:
                 prints('Invalid range:', c, file=sys.stderr)
                 raise SystemExit(1)
@@ -274,7 +274,7 @@ def main(args):
                 parts = tuple(map(conv_code, parts))
             for i in parts:
                 not_single(i)
-            ranges.add(tuple(parts))
+            ranges.add(parts)
         else:
             if opts.codes:
                 c = conv_code(c)