Handle single keyword metadata on namespace name

Namespace symbols within the `ns` macro can have metadata - this is, for example, used by lein when running only a subset of tests with `lein test :keyword`.

A ns declaration might look like:
```clojure
(ns ^:interation ^{:slow false :skip-coverage true}
  my-namespace-name
  (:use ...))
```

The ^{} is already somewhat handled by `fireplace#ns()`, but the single keyword case breaks ns name detection.