Add wrapped timed_deplete method for providing process time

Simple wrapper function that passes all arguments to
openmc.deplete.integrator.deplete and returns a two-item
tuple. The first item is the process time spent depleting
all materials (can be on one of many MPI processes).
The second item is what is returned directly from the
deplete function.

openmc/deplete/integrator/cram.py

@@ -53,6 +53,25 @@ def deplete(chain, x, rates, dt, print_out=True, matrix_func=None):
     return x_result
 
 
+def timed_deplete(*args, **kwargs):
+    """Wrapper over :func:`deplete` that also returns process time
+
+    All arguments and keyword arguments are passed onto
+    :func:`deplete` directly.
+
+    Returns
+    -------
+    proc_time: float
+        Process time required to return from deplete
+    results: list of numpy arrays
+        Output from :func:`deplete` call
+    """
+
+    start = time.time()
+    results = deplete(*args, **kwargs)
+    return time.time() - start, results
+
+
 def _cram_wrapper(chain, n0, rates, dt, matrix_func=None):
     """Wraps depletion matrix creation / CRAM solve for multiprocess execution