More library-compat fixes from porting the examples (markdown, malli)

Reader / loader:
- #?@ splicing reader conditionals now actually splice the matched collection's
  items into the enclosing sequence; the splice flag was read but ignored, so a
  binding vector like [a #?@(:clj [b (.foo b)])] lost its alignment.
- the file loader reads by position and skips a top-level form that reads as
  nothing (a :cljs-only #?, a #_ discard, a trailing comment) instead of
  treating it as EOF — which silently dropped the rest of a large .cljc file.
- jolt's reader feature set now includes :clj (was {:jolt :default}). jolt is a
  Clojure/JVM-compatible host that emulates clojure.lang.* and java.* interop,
  so it reads the :clj branch of a .cljc library, not :cljs. This also lets four
  more reader-conditional corpus cases pass (floor 2726 -> 2730).

Backend:
- munge-name escapes ' (prime) -> _PRIME_; a Clojure symbol like f' otherwise
  emitted a bare ' into Scheme, which is the quote reader macro and unbalanced
  the output.

Host shims:
- clojure.java.io/writer (pass through a StringWriter, file-back a path) and a
  readLine on the string reader, so line-seq over (io/reader …) works (markdown).

A better "unsupported destructuring pattern: <pat>" error message.

host/chez/run-corpus.ss

@@ -11,7 +11,7 @@
 ;; reset between cases so there is no leakage — same isolation a fresh process gives.
 ;;
 ;;   chez --script host/chez/run-corpus.ss
-;;   JOLT_CHEZ_ZJ_FLOOR=N   override the regression floor (default 2726)
+;;   JOLT_CHEZ_ZJ_FLOOR=N   override the regression floor (default 2730)
 ;;   JOLT_CORPUS_LIMIT=N    every-Nth stride (fast iteration; floor drops to 0)
 ;;   JOLT_DUMP_CRASH_LABELS=1   list crash + allowlisted labels
 (import (chezscheme))
@@ -196,7 +196,7 @@
 
 ;; Regression floor: fail on any NEW divergence or if pass drops below the floor.
 (define base-floor (let ((s (getenv "JOLT_CHEZ_ZJ_FLOOR")))
-                     (if s (string->number s) 2726)))
+                     (if s (string->number s) 2730)))
 (define floor (if limit 0 base-floor))
 (when (or (> (length diverged) 0) (< pass floor))
   (printf "REGRESSION: pass ~a < floor ~a or ~a new divergence(s)\n"