Fix mixed units assemblies to work, regardless of project settings (#5818)

* Add mixed units test

* Add incorrect output

* Change to always set units since old units are not accurate

* Update output after fix

rust/kcl-lib/tests/assembly_mixed_units_cubes/input.kcl

@@ -0,0 +1,8 @@
+@settings(defaultLengthUnit = in)
+
+
+import "cube-inches.kcl" as cubeIn
+import "cube-mm.kcl" as cubeMm
+
+cubeIn
+cubeMm