feat(strictness): seq/shuffle/NaN?/nthrest/nthnext reject bad args

- seq throws on non-seqables (numbers/functions); collections/strings/nil ok
- shuffle requires a collection (throws on numbers/strings/nil)
- NaN? throws on non-numbers
- nthrest/nthnext require a numeric count (nil count throws), clamp negative
  counts to the whole coll, and treat a nil coll as nil
- update inherits assoc's vector bounds/keyword-key checks

nan_qmark clean; shuffle 9/1; nthrest 13/1; nthnext 12/0/1; update 59/2/2.
clojure-test-suite pass 3880->3889. spec: seq/strictness-round-3 (14). jpm test green.

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

@@ -18,7 +18,7 @@
 
 # Baseline: assertions Jolt currently passes across the suite. Raise as Jolt
 # improves so a regression (previously-passing assertion breaking) is caught.
-(def baseline-pass 3875)
+(def baseline-pass 3885)
 # A file is "clean" when it ran with zero failures AND zero errors.
 (def baseline-clean-files 45)
 # Per-file wall-clock budget (seconds). Normal files finish in well under 1s;

test/spec/sequences-spec.janet

@@ -179,3 +179,21 @@
   ["assoc odd args"     :throws "(assoc {:a 1} :b)"]
   ["assoc on number"    :throws "(assoc 5 :a 1)"]
   ["assoc on set"       :throws "(assoc #{} :a 1)"])
+
+# Strictness on more core fns: seq/shuffle need seqables, NaN? needs a number,
+# nthrest/nthnext need a numeric count (and clamp negatives / accept nil coll).
+(defspec "seq / strictness round 3"
+  ["seq on number"      :throws "(seq 1)"]
+  ["seq on fn"          :throws "(seq (fn [] 1))"]
+  ["seq vector ok"      "[1 2]" "(seq [1 2])"]
+  ["NaN? on nil"        :throws "(NaN? nil)"]
+  ["NaN? on number ok"  "false" "(NaN? 1.0)"]
+  ["shuffle on number"  :throws "(shuffle 1)"]
+  ["shuffle on string"  :throws "(shuffle \"abc\")"]
+  ["shuffle vec ok"     "3"     "(count (shuffle [1 2 3]))"]
+  ["nthrest nil count"  :throws "(nthrest [0 1 2] nil)"]
+  ["nthrest negative"   "[0 1 2]" "(nthrest [0 1 2] -1)"]
+  ["nthrest nil coll"   "nil"   "(nthrest nil 0)"]
+  ["nthnext nil count"  :throws "(nthnext [0 1 2] nil)"]
+  ["update vec oob"     :throws "(update [] 1 identity)"]
+  ["update vec kw key"  :throws "(update [1 2 3] :k identity)"])