Fix footprint return type of get_runtime_config

This is arguably one of those places where static type checking
and python do not play particually well together, but this does
allow mypy to report all is well.

The issue here is that the optional command line argument 'footprint'
results in get_runtime_config getting hold of values for PUE and
jobinfo. These are used by carbonFootprint.py's
get_footprint_reduction_estimate. If footprint is not passed in
we should return some null value. The presence of the same command
line argument is checked in main before dispatching to
get_footprint_reduction_estimate so it does not really matter
what those values are if footprint is not selected. It feels
"pythonic" to return None, but get_footprint_reduction_estimate
cannot handle None so mypy is unhappy. Instead we return 'zero'
values in the "correct" types.

A better solution, probably, would be to bundle jobinfo and PUE into
a container of some sort that can be tested in main
and passed into get_footprint_reduction_estimate.

cats/configure.py

@@ -13,7 +13,7 @@
 import logging
 import sys
 from collections.abc import Mapping
-from typing import Any
+from typing import Any, Union
 
 import requests
 import yaml
@@ -24,7 +24,8 @@
 __all__ = ["get_runtime_config"]
 
 
-def get_runtime_config(args) -> tuple[dict, APIInterface, str, int]:
+def get_runtime_config(args) -> tuple[APIInterface, str, int, 
+                                      list[tuple[int, float]],float]:
     """Return the runtime cats configuration from list of command line
     arguments and content of configuration file.
 
@@ -61,8 +62,13 @@ def get_runtime_config(args) -> tuple[dict, APIInterface, str, int]:
         jobinfo = get_job_info(args, configmapping["profiles"])
         PUE = configmapping["PUE"]
     else:
-        jobinfo = None
-        PUE = None
+        # Here we return zero values of the correct type rather than
+        # None so that static typing allows our return type to match
+        # the input to get_footprint_reduction_estimate(). However,
+        # we call that function inside a args.footprint conditional so
+        # we should never see these values in that function. 
+        jobinfo = [(0, 0.0)]
+        PUE = 0.0
 
     return CI_API_interface, location, duration, jobinfo, PUE