Step 5: partition-by, dedupe → lazy overlay + trampoline/rand-int overlay

partition-by (10-seq.clj): ported canonical lazy implementation
from CLJS — lazy-seq + cons + take-while, matching Clojure/CLJS
exactly. Fixes the third and final remaining leak from Step 3.

dedupe (20-coll.clj): replaced eager vec-based impl with lazy
step function using lazy-seq + cons. Infinite input no longer hangs.

trampoline (20-coll.clj): pure HOF ported from CLJS — recur until
non-function result. Removed core-trampoline + binding from Janet.

rand-int (20-coll.clj): thin overlay over Janet math/random +
math/floor. Removed core-rand-int + binding from Janet.

Removed core-partition-by + binding from core.janet (now in overlay).

Tests: added dedupe infinite-input case to lazy-infinite harness.
22/22 pass. Conformance 229x3. Specs 32/32.

test/integration/lazy-infinite-test.janet

@@ -55,6 +55,7 @@
    ["take 6 mapcat dup range"             "(quote (0 0 1 1 2 2))" "(take 6 (mapcat (fn [x] [x x]) (range)))"]
    ["first rest lazy"                     "1"                     "(let [[a & r] (range)] (first r))"]
    ["take 3 rest lazy"                    "(quote (1 2 3))"       "(let [[a & r] (range)] (take 3 r))"]
+   ["dedupe inf"             "(quote (1 2 1 2 1))" "(take 5 (dedupe (cycle [1 1 2 2])))"]
    ["take 3 take-nth 2 range"             "(quote (0 2 4))"       "(take 3 (take-nth 2 (range)))"]
    ["take 3 interpose :x range"           "(quote (0 :x 1))"       "(take 3 (interpose :x (range)))"]
    ["take 3 map vector range iterate"     "(quote ([0 100] [1 101] [2 102]))" "(take 3 (map vector (range) (iterate inc 100)))"]