major array pack and flatten update (closes #48)

- dimensions flattening conversion only flattens packed dimensions
- conversion for packing arrays when necessary (preserves memories)
- added coverage for array with multiple packed dimensions
- test runner no longer forbids multi-dim accesses after conversion
- Decl and subordinate types derive Ord

test/basic/packed_array.sv

@@ -0,0 +1,14 @@
+module top;
+    logic [2:0][3:0] arr [1:0];
+    initial begin
+        for (int i = 0; i <= 1; i++) begin
+            for (int j = 0; j <= 2; j++) begin
+                for (int k = 0; k <= 3; k++) begin
+                    $display("%b", arr[i][j][k]);
+                    arr[i][j][k] = 1'(i+j+k);
+                    $display("%b", arr[i][j][k]);
+                end
+            end
+        end
+    end
+endmodule