Add behavioral spec suites for the collection API (~180 cases). Writing them
surfaced and fixed real bugs:
- (count nil) errored; now 0 (Clojure semantics)
- (repeat x) and (repeatedly f) — the infinite 1-arg arities — were unsupported;
now return lazy infinite seqs
- set equality used deep= (representation-sensitive), so a set of map literals
could differ from an equal set built differently; now value-based (each
element value-equal to some element of the other)
Known limitation filed: phm-typed maps (from hash-map) used as set elements /
map keys hash by identity (map *literals* are structs and work).
jpm test green.
