Transients mutate in-place on persistent ops

[frenchy64]

I think it's just assoc and dissoc.

;; jank
clojure.core=> (assoc (transient {}) 1 2)
transient_hash_map@0x10ff4aae0

user=>  (assoc (transient {}) 1 2)
Execution error (ClassCastException) at user/eval1 (REPL:1).
class clojure.lang.PersistentArrayMap$TransientArrayMap cannot be cast to class clojure.lang.Associative (clojure.lang.PersistentArrayMap$TransientArrayMap and clojure.lang.Associative are in unnamed module of loader 'app')