Close the remaining Phase-2 stdlib parity gaps.
clojure.set: pure Clojure over core, so just added to the prelude stdlib tier
(driver.janet stdlib-ns-files + jolt-chez fingerprint), same as clojure.edn.
clojure.math: not a .clj on the seed (native math/ bindings via jolt-h79), so
Chez gets its own host/chez/math.ss def-var!ing each fn over Chez native flonum
math. The analyzer already knows the ns (api.janet install-clojure-math!), so
refs lower to var-deref. Also adds the missing 'long' coercion to converters.ss
(int's sibling; several math cases wrap in long).
clojure.pprint: dropped the 2-arity's (binding [*out* writer] ...). *out* isn't
a bindable var in jolt — printing routes through the host (dyn :out) seam, so
the binding never redirected anything; it only made the defn uncompilable, which
the seed tolerated via interpreter fallback. Chez has no fallback, so the whole
pprint defn died. Dropping it is behavior-preserving (writer was always ignored)
and lets pprint compile cleanly. Both corpus cases pass.
Corpus parity 2259 -> 2280, crashes 191 -> 170, 0 new divergences. Floor raised.
New unit test test/chez/_stdlib.janet (27/27). Full Janet gate green (147 files).
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