fix: case composite constants, associative?/reversible?, update non-fn args, nth nil

- case: quote list literals (read as arrays) in constant position so a wrapped
  list ((a b c)) matches by value instead of being evaluated as a call; symbol
  constants already quoted. Vector/map/set constants already worked. case errors
  in the suite drop to 0 (60 pass).
- associative?: true only for vectors (pvec) and maps (phm/struct/sorted-map),
  not lists/tuples-from-seq-fns/lazy-seqs/sets.
- reversible?: true for vectors and sorted-map/sorted-set only.
- update: coerce f via as-fn so (update m k :kw)/(update m k a-set) work; extra
  args already handled.
- nth: (nth nil i)/(nth nil i default) returns nil/default instead of throwing.

clojure-test-suite pass 3649->3678, errors 122->105, clean files 44->46.
associative?/reversible? files now fully clean. spec: predicates + control/case.
jpm test green.

test/integration/clojure-test-suite-test.janet

@@ -18,9 +18,9 @@
 
 # Baseline: assertions Jolt currently passes across the suite. Raise as Jolt
 # improves so a regression (previously-passing assertion breaking) is caught.
-(def baseline-pass 3600)
+(def baseline-pass 3660)
 # A file is "clean" when it ran with zero failures AND zero errors.
-(def baseline-clean-files 43)
+(def baseline-clean-files 45)
 # Per-file wall-clock budget (seconds). Normal files finish in well under 1s;
 # this only fires on infinite-sequence hangs.
 (def per-file-timeout 6)