feat(strictness): assoc bounds, dissoc/count map-only, subvec bounds, numerator/denominator, min-key empty

- assoc on a vector bounds-checks the index (0..count); out-of-range/negative throw
- dissoc throws on non-maps (numbers/sequences/sets/scalars); nil ok; records/
  sorted-maps/meta-maps still handled
- count throws on scalars (numbers/keywords/symbols/booleans/chars)
- subvec validates vector type and 0<=start<=end<=count
- numerator/denominator always throw (Jolt has no ratio type)
- min-key/max-key throw on no values

count 18/2; dissoc 19/3; assoc 36/6; subvec 26/3/5; numerator/denominator throw
cases pass. clojure-test-suite pass 3840->3864. spec: map/strictness (16). 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 3835)
+(def baseline-pass 3860)
 # 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;