feat: mf_dttm macro and associated test

tests/crossplatform/mf_dttm.test.sas

@@ -0,0 +1,22 @@
+/**
+  @file
+  @brief Testing mf_dttm macro
+
+  <h4> SAS Macros </h4>
+  @li mf_dttm.sas
+  @li mp_assert.sas
+  @li mp_assertscope.sas
+
+**/
+
+%global test1;
+
+%mp_assertscope(SNAPSHOT)
+%let test1=%mf_dttm();
+%mp_assertscope(COMPARE,ignorelist=test1)
+
+%mp_assert(
+  iftrue=("&test1"="DATETIME19.3" or "&test1"="E8601DT26.6"),
+  desc=Basic test,
+  outds=work.test_results
+)