Fix namespaced symbols in syntax quoted binding vector

[yuhan0]

These underscores in a syntax quoted form cause the macroexpansion to contain the following technically invalid binding forms (even if deftype accepts it without complaining)

(clojure.core/deftype ...
  (meta [potemkin.collections/_] ...)
  (with-meta [potemkin.collections/_ x__1234__auto__] ...)
  ...)

[slipset]

Could I ask you to add a test which demonstrates the breaking prior to this fix, and that passes after this fix?

[yuhan0]

I don't think there are any observed breakages due to the prior behaviour, because clojure.core.deftype is lenient enough to accept a binding vector with namespaced symbols.

(deftype Foo []
  Object
  (toString [invalid/binding]
    "no error"))

This PR simply makes the output more robust, in case tooling or future versions decide to treat this as invalid.