core: fix jolt-r81 at root — move lazy-seq/lazy-cat to the early syntax tier

Root cause: lazy-seq/lazy-cat were defined in 30-macros, which loads AFTER the
seq/coll tiers (10-seq, 20-coll) that use them. In compile mode a tier's forms
are compiled as the tier loads, so (lazy-seq …) in those tiers was compiled when
lazy-seq was not yet a registered macro — i.e. as a CALL to the macro-as-function,
which at runtime returns its own expansion `(make-lazy-seq (fn* [] …))` as data.
That leaked form then flowed into ops like `odd?` (partition-by) → type errors,
or silently produced wrong structure. Interpret/self-host masked it (expand at
call time); the eager fallbacks and the earlier letfn versions masked it by
falling back to the interpreter.

Fix: define lazy-seq/lazy-cat in 00-syntax (loaded first), exactly as when-let
already is for the same reason. They use only seed fns (make-lazy-seq/coll->cells/
concat) + map. With the macro registered early, the seq/coll tiers compile
(lazy-seq …) correctly.

With the root fixed, interleave/reductions/tree-seq drop their letfn workarounds
and use the canonical recursive Clojure forms (top-level / fn-self-name recursion
inside lazy-seq), verified leak-free in compile mode with strict probes.

Regression guards added: partition-by with odd? (the strict pred that exposed the
leak; the prior case used identity which masked it), reductions over an infinite
range, tree-seq summed through a strict filter — all ×3 modes.

Gate: conformance 249x3, lazy-infinite 40/40, fixpoint, self-host, specs+unit green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/integration/conformance-test.janet

@@ -152,6 +152,11 @@
    ["reductions"      "(quote (1 3 6 10))" "(reductions + [1 2 3 4])"]
    ["reductions init" "(quote (0 1 3 6))" "(reductions + 0 [1 2 3])"]
    ["dedupe"          "(quote (1 2 3 1))" "(dedupe [1 1 2 3 3 1])"]
+   # partition-by with a strict pred (odd?) — guards jolt-r81: a lazy overlay fn
+   # whose lazy-seq leaked its expansion in compile mode passed a non-int to odd?.
+   ["partition-by odd?" "(quote ((1 1) (2) (3 3)))" "(partition-by odd? [1 1 2 3 3])"]
+   ["reductions inf"  "(quote (0 1 3 6))" "(take 4 (reductions + (range)))"]
+   ["tree-seq strict" "10"  "(reduce + 0 (filter (complement coll?) (tree-seq coll? seq [1 [2 [3 4]]])))"]
    ["keep-indexed"    "(quote (:b :d))" "(keep-indexed (fn [i x] (if (odd? i) x)) [:a :b :c :d])"]
    ["map-indexed"     "(quote ([0 :a] [1 :b]))" "(map-indexed (fn [i x] [i x]) [:a :b])"]
    ["trampoline"      ":done"         "(do (defn a [n] (if (zero? n) :done (fn [] (a (dec n))))) (trampoline a 5))"]