[WIP] relocate.py: parallelize test replacement logic (#19690)

* sbang pushed back to callers;
star moved to util.lang

* updated unit test

* sbang test moved; local tests pass

Co-authored-by: Nathan Hanford <hanford1@llnl.gov>

lib/spack/llnl/util/lang.py

@@ -673,6 +673,13 @@ def uniq(sequence):
     return uniq_list
 
 
+def star(func):
+    """Unpacks arguments for use with Multiprocessing mapping functions"""
+    def _wrapper(args):
+        return func(*args)
+    return _wrapper
+
+
 class Devnull(object):
     """Null stream with less overhead than ``os.devnull``.