feat: distinguish map entries from vectors; min-key NaN ordering; subvec float coercion

- A map entry is a 2-element tuple (Jolt produces tuples only from map iteration;
  vector literals are pvecs, lists are arrays). key/val/map-entry? now accept a
  2-tuple and reject a plain vector, matching Clojure's MapEntry-vs-vector
  distinction — no metadata needed, the representations already differ.
- min-key/max-key reproduce Clojure's NaN-aware folding (2-arg strict </>, then
  <=/>=) and require numeric keys (NaN allowed, strings throw).
- subvec coerces float/NaN indices like (int ...) (truncate, NaN->0) then
  bounds-checks, instead of throwing on non-integers.

min_key 35/14 -> 49/0 (clean); key/val recover the 2-vector cases; subvec floats
fixed. clojure-test-suite pass 3898->3921. Updated conformance-test (key/val now
needs a real entry). spec: map/map-entry-&-key-ordering (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 3895)
+(def baseline-pass 3915)
 # 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;