New collection tier (core/20-coll.clj): six pure, eager fns expressed as
compositions of frozen primitives (reduce/assoc/get/conj/filter/vec). Six more
core-* primitives + table entries gone from the Janet kernel.
Two semantics to preserve, caught by the suite:
- max-key/min-key use the canonical multi-arity form (strict </> on the first
pair, <=/>= in the fold) to reproduce the JVM IEEE-754 NaN behavior; a single
reduce got the NaN cases wrong.
- frequencies/group-by base on (hash-map), not the {} literal: a struct map
doesn't canonicalize collection keys across representations ({:a 1} literal vs
(hash-map :a 1)), a PHM does — same reason the Janet impl used make-phm.
Conformance 218/218 all modes; battery holds 3916.
57b8ffcb9b