d2ir: Fix variables to passthrough primary type

If the variable is a number it should be parsed as a number and not coerced into a string.
See test change.

d2ir/compile.go

@@ -203,8 +203,12 @@ func (c *compiler) resolveSubstitutions(varsStack []*Map, node Node) {
 						n.Primary_ = nil
 					}
 				} else {
-					s.Value[i].String = go2.Pointer(resolvedField.Primary().Value.ScalarString())
-					subbed = true
+					if i == 0 && len(s.Value) == 1 {
+						node.Primary().Value = resolvedField.Primary().Value
+					} else {
+						s.Value[i].String = go2.Pointer(resolvedField.Primary().Value.ScalarString())
+						subbed = true
+					}
 				}
 				if resolvedField.Composite != nil {
 					switch n := node.(type) {

d2ir/import_test.go

@@ -157,7 +157,7 @@ label: meow`,
 					"a.d2":     "vars: { x: 2 }; hi: ${x}",
 				})
 				assert.Success(t, err)
-				assertQuery(t, m, 0, 0, "2", "hi")
+				assertQuery(t, m, 0, 0, 2, "hi")
 			},
 		},
 		{
@@ -168,7 +168,7 @@ label: meow`,
 					"a.d2":     "vars: { x: 2 }",
 				})
 				assert.Success(t, err)
-				assertQuery(t, m, 0, 0, "1", "hi")
+				assertQuery(t, m, 0, 0, 1, "hi")
 			},
 		},
 	}