test: fix test where metric teaspoons are compared to mL and add check on US teaspoons vs mL

examples/tests/unit_consistency_misc.nbt

@@ -17,7 +17,8 @@ assert_eq(1 gregorian_year, 365.2425 day)
 assert_eq(1 julian_year, 365.25 day)
 assert_eq(1 year, 1 tropical_year)
 
-assert_eq(1 teaspoon, 5 mL, 1e-5 teaspoon)
+assert_eq(1 metric_teaspoon, 5 mL, 1e-5 metric_teaspoon)
+assert_eq(1 teaspoon, 4.92892159375 mL, 1e-5 teaspoon)
 assert_eq(3 teaspoon, 1 tablespoon, 1e-5 teaspoon)
 
 assert_eq(1 gallon, 231 inch³, 1e-5 inch³)