Library ports: get hiccup running, verify malli (reader + interop fixes) (#127)

* Reader: #() params survive syntax-quote (auto-gensym names)

#(...) named its synthesized params with bare gensyms, so a #() written inside a
syntax-quote had its params qualified to the current ns by sq-symbol — and a
qualified symbol isn't a valid fn param. hiccup's compiler emits
`(let [sb# ..] (iterate! #(.append sb# %) ..)), which broke with "Unable to
resolve symbol: ns/_NNNN".

Name the params with a trailing # (auto-gensym suffix, like Clojure's p1__N#) so
syntax-quote maps them consistently and leaves them unqualified. Harmless outside
a backtick (just a regular symbol name).

* interop: String/valueOf static + String is a CharSequence

Two interop gaps surfaced bringing up hiccup and malli:
- String/valueOf(Object): hiccup's compiler stringifies attribute values with
  (String/valueOf (or arg "")). Added the static — "null" for nil, else core-str.
- (instance? CharSequence s) returned false for a string; String implements
  CharSequence, and malli's :re validator gates on it before matching, so :re
  schemas always failed. instance-check now answers true for strings.

---------

Co-authored-by: Yogthos <yogthos@gmail.com>

test/spec/host-interop-spec.janet

@@ -79,6 +79,14 @@
   [".charAt"        "\\b"     "(.charAt \"abc\" 1)"]
   [".equalsIgnoreCase" "true" "(.equalsIgnoreCase \"AbC\" \"aBc\")"]
   ["Long/MAX_VALUE" "true"    "(pos? Long/MAX_VALUE)"]
+  # String/valueOf static (jolt-nkx): hiccup stringifies attribute values with it.
+  ["String/valueOf num"  "\"42\""   "(String/valueOf 42)"]
+  ["String/valueOf str"  "\"hi\""   "(String/valueOf \"hi\")"]
+  ["String/valueOf kw"   "\":k\""   "(String/valueOf :k)"]
+  ["String/valueOf nil"  "\"null\"" "(String/valueOf nil)"]
+  # String implements CharSequence (malli's :re gates on it, jolt-ltwk).
+  ["instance? CharSequence" "true"  "(instance? CharSequence \"aaa\")"]
+  ["instance? CharSequence non-str" "false" "(instance? CharSequence 42)"]
   ["unsupported method throws" :throws "(.frobnicate \"abc\")"])
 
 # java.time shims (jolt-ea7): epoch-ms backed values + a DateTimeFormatter