Add support for persistent hash map formatting

[ilmoraunio]

Fixes a finding from the latest generative test run:

No method in multimethod 'format-value' for dispatch value: class clojure.lang.PersistentHashMap

The offending (reduced) payload being:

(gql '(("Px6yr3Z6"
         {:arguments {"I58LwWPr5" {"BnX8" 2,
                                   :F {},
                                   "mfvh" true,
                                   "Gx7uc" [],
                                   :l nil,
                                   :b {},
                                   "v9SN" nil,
                                   "Qpe41O8j" "304P44x3X",
                                   :gF5 :v,
                                   "m" {}}}})))

The fix was to implement format-value for hash maps using the same implementation as for array maps.