Implement user-configurable random number stride (#3067)

Co-authored-by: Paul Romano <paul.k.romano@gmail.com>

docs/source/io_formats/settings.rst

@@ -538,6 +538,15 @@ pseudo-random number generator.
 
   *Default*: 1
 
+--------------------
+``<stride>`` Element
+--------------------
+
+The ``stride`` element is used to specify how many random numbers are allocated
+for each source particle history.
+
+  *Default*: 152,917
+
 .. _source_element:
 
 --------------------

docs/source/io_formats/statepoint.rst

@@ -23,6 +23,7 @@ The current version of the statepoint file format is 18.1.
                bank is present (1) or not (0).
 
 :Datasets: - **seed** (*int8_t*) -- Pseudo-random number generator seed.
+           - **stride** (*uint64_t*) -- Pseudo-random number generator stride.
            - **energy_mode** (*char[]*) -- Energy mode of the run, either
              'continuous-energy' or 'multi-group'.
            - **run_mode** (*char[]*) -- Run mode used, either 'eigenvalue' or