feat(strictness): first/rseq shape checks, assoc even-args + non-associative

- first throws on scalars (numbers/keywords/booleans/char & symbol structs)
- rseq is vector/sorted-only (throws on strings/maps/numbers/seqs)
- assoc requires an even kv count and a map/vector/nil receiver

first clean; rseq 12/1; assoc 39/3. clojure-test-suite pass 3864->3874.
spec: seq/more-strictness (11). 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 3860)
+(def baseline-pass 3870)
 # 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;