Chez parity: STM stub + portable line-seq (janet.* audit, jolt-0obq)

Audit of the janet.*/jolt.interop/STM corpus cases vs Chez equivalents: the Janet
FFI-bridge cases (janet/string, janet/type, janet.math/sqrt, janet.string/ascii-
upper) test functionality already covered by PORTABLE corpus cases (str 29, type 9,
sqrt 3, upper-case 9), so they're safe to delete in Phase 5. Two needed a Chez
equivalent so they pass instead of being lost:

- clojure.lang.LockingTransaction/isRunning -> false (no STM on jolt).
- line-seq: the corpus case used janet/spit setup but was the SOLE line-seq
  coverage (0 other cases). Ported janet/spit->spit, and added a native Chez
  line-seq (drain a jhost io/reader + split on newline; no trailing empty line)
  that delegates a Janet map-reader to the overlay version.

zero-Janet 2694->2696, prelude floor 2648; self-host + Janet gate + JVM cert green.

jolt-cf1q.7 jolt-0obq

test/chez/run-corpus-zero-janet.janet

@@ -219,7 +219,7 @@
 # 2685; deftype (P. args) constructor via host-new var fallback -> 2688;
 # date/time (Date/Timestamp/SimpleDateFormat/TimeZone) + clojure.edn/read over a
 # reader -> 2692.
-(def base-floor (scan-number (or (os/getenv "JOLT_CHEZ_ZJ_FLOOR") "2694")))
+(def base-floor (scan-number (or (os/getenv "JOLT_CHEZ_ZJ_FLOOR") "2696")))
 (def floor (if (os/getenv "JOLT_CORPUS_LIMIT") 0 base-floor))
 (when (or (> (length diverged) 0) (< pass floor))
   (printf "REGRESSION: pass %d < floor %d or %d new divergence(s)" pass floor (length diverged)))