fix(keyword data): optional keywords (#1920)

Flopy allows some keywords to be excluded from recarrays, like "FILEIN".  This fix makes sure that optional keywords, like "MIXED" are not excluded from recarrays.  Since they are optional their presence adds information to the recarray and they therefore can not be excluded.

Co-authored-by: scottrp <45947939+scottrp@users.noreply.github.com>

autotest/test_mf6.py

@@ -2187,6 +2187,20 @@ def test_multi_model(function_tmpdir):
         assert rec_array[0][3] == model_names[1]
         assert rec_array[1][1] == "transport.ims"
         assert rec_array[1][2] == model_names[2]
+    # test ssm fileinput
+    gwt2 = sim2.get_model("gwt_model_1")
+    ssm2 = gwt2.get_package("ssm")
+    fileinput = [
+        ("RCH-1", f"gwt_model_1.rch1.spc"),
+        ("RCH-2", f"gwt_model_1.rch2.spc"),
+        ("RCH-3", f"gwt_model_1.rch3.spc", "MIXED"),
+        ("RCH-4", f"gwt_model_1.rch4.spc"),
+    ]
+    ssm2.fileinput = fileinput
+    fi_out = ssm2.fileinput.get_data()
+    assert fi_out[2][1] == "gwt_model_1.rch3.spc"
+    assert fi_out[1][2] is None
+    assert fi_out[2][2] == "MIXED"
 
     # create a new gwt model
     sourcerecarray = [("WEL-1", "AUX", "CONCENTRATION")]

flopy/mf6/data/mfdatastorage.py

@@ -2857,6 +2857,7 @@ def build_type_list(
                     if (
                         data_item.type != DatumType.keyword
                         or data_set.block_variable
+                        or data_item.optional
                     ):
                         initial_keyword = False
                         shape_rule = None