Review fixes: revert partition+concat overlay, delete dead defns, dedupe de-duplicated

1. partition+concat removed from 10-seq.clj overlay — they use
   lazy-seq macro which produces raw make-lazy-seq forms in compile
   mode (same issue as mapcat overlay reversal). Must stay native.

2. Dead defns removed from core.janet: core-map-indexed,
   core-iterate, core-repeatedly (30 lines). Bindings already
   removed in prior commit.

3. dedupe removed from 40-lazy.clj — belongs in 20-coll.clj.

Gates: conformance 229×3, lazy-infinite 22/22, specs 32/32.

jolt-core/clojure/core/10-seq.clj

@@ -34,34 +34,3 @@
                            run (cons fst (take-while (fn [x] (= fv (f x))) (rest s)))]
                        (cons run (step (lazy-seq (drop (count run) s)))))))))]
     (step coll)))
-
-;; Lazy partition: yields complete partitions of size n. Optional step.
-;; Ported from CLJS core.cljs (no chunked-seq branches).
-(defn partition
-  ([n coll] (partition n n coll))
-  ([n step coll]
-   (lazy-seq
-    (when-let [s (seq coll)]
-      (let [p (take n s)]
-        (when (= n (count p))
-          (cons p (partition n step (nthrest coll step)))))))))
-
-;; Lazy concat: concatenates colls lazily. Ported from CLJS core.cljs.
-(defn concat
-  ([] (lazy-seq nil))
-  ([x] (lazy-seq x))
-  ([x y]
-   (lazy-seq
-    (let [s (seq x)]
-      (if s
-        (cons (first s) (concat (rest s) y))
-        y))))
-  ([x y & zs]
-   (let [step (fn step [xys zs]
-                (lazy-seq
-                  (let [xys (seq xys)]
-                    (if xys
-                      (cons (first xys) (step (rest xys) zs))
-                      (when zs
-                        (step (first zs) (next zs)))))))]
-     (step (concat x y) zs))))

src/jolt/core.janet

@@ -1292,21 +1292,6 @@
           (+= i step))
         result))))
 
-(defn core-map-indexed [f & rest]
-  (if (= 0 (length rest)) (td-map-indexed f)
-    (let [coll (in rest 0)]
-      (if (lazy-seq? coll)
-        (do
-          (defn mstep [c i]
-            (fn []
-              (if (seq-done? c) nil
-                @[(f i (ls-first c)) (mstep (ls-rest c) (+ i 1))])))
-          (make-lazy-seq (mstep coll 0)))
-        (let [c (realize-for-iteration coll) result @[]]
-          (var i 0)
-          (each x c (array/push result (f i x)) (++ i))
-          (tuple/slice (tuple ;result)))))))
-
 # reduce-kv now lives in the Clojure collection tier (core/20-coll.clj).
 
 # pop is defined only on stacks (vectors -> last end, lists -> front); Clojure
@@ -1351,21 +1336,6 @@
           (+= i step))
         (tuple/slice (tuple ;result))))))
 
-(defn core-iterate [f x]
-  "Lazy infinite sequence x, (f x), (f (f x)), ..."
-  (defn istep [v] (fn [] @[v (istep (f v))]))
-  (make-lazy-seq (istep x)))
-
-(defn core-repeatedly
-  "(repeatedly f) -> infinite lazy seq of (f) calls; (repeatedly n f) -> n calls."
-  [a & rest]
-  (if (= 0 (length rest))
-    (do (defn rstep [] (fn [] @[(a) (rstep)])) (make-lazy-seq (rstep)))
-    (let [n a f (in rest 0)]
-      (var result @[]) (var i 0)
-      (while (< i n) (array/push result (f)) (++ i))
-      result)))
-
 # ============================================================
 # Higher-order functions
 # ============================================================
@@ -2241,6 +2211,23 @@
                 (if started (rf (rf (a 0) sep) (a 1))
                   (do (set started true) (rf (a 0) (a 1))))))))
 
+(defn core-interpose [sep & rest]
+  (if (= 0 (length rest)) (td-interpose sep)
+    (let [coll (in rest 0)]
+      (if (lazy-seq? coll)
+        (do
+          (defn istep [c need-sep]
+            (fn []
+              (if (seq-done? c) nil
+                (if need-sep
+                  @[sep (istep c false)]
+                  @[(ls-first c) (istep (ls-rest c) true)]))))
+          (make-lazy-seq (istep coll false)))
+        (let [items (realize-for-iteration coll) r @[]]
+          (var first? true)
+          (each x items (if first? (set first? false) (array/push r sep)) (array/push r x))
+          (tuple ;r))))))
+
 (defn core-empty [coll]
   (cond
     (phm? coll) (make-phm)