Numeric operators misbehave when in unary position

When we use `+`, `*`, etc. (including the promotion operators) jank doesn't make sure that the passed in values are actually numeric.

```jank
user=> (* :k)
:k
```

While Clojure attempts to cast the passed in value to a `java.lang.Number`.

```clj
user=> (* :k)
Execution error (ClassCastException) at java.lang.Class/cast (Class.java:3492).
Cannot cast clojure.lang.Keyword to java.lang.Number
```