core: variadic bit ops, set? covers sorted sets, if rejects extra forms

Three canonical-conformance fixes from the post-shrink batch:

- bit-and/bit-or/bit-xor/bit-and-not get Clojure's variadic arities as
  20-coll shells folding the binary host ops (now __bit-* seams). 2-arg call
  sites still compile to the native janet op via the backend's native-ops
  table. The passes.clj constant-fold table now names the seams — the public
  fns are overlay and don't exist when the compiler loads (this briefly broke
  every compile-mode init).

- core-set? recognizes the :jolt/sorted-set representation (jolt-dpn):
  (set? (sorted-set 1)) was false, and ifn? on sorted sets inherited the bug.

- (if) / (if test) / (if test then else extra) throw in both the analyzer
  and the interpreter — spec 03-special-forms X1, now marked verified.

Suite 4704 -> 4706; bench and the greeter example benchmark are flat.

src/jolt/core.janet

@@ -1450,7 +1450,8 @@
 (defn core-hash-set [& xs]
   (apply make-phs xs))
 
-(defn core-set? [x] (set? x))
+# sorted sets are tagged tables the host set? predicate misses (jolt-dpn)
+(defn core-set? [x] (or (set? x) (core-sorted-set? x)))
 (defn core-disj [s & ks]
   (cond
     (core-sorted-set? s) ((sorted-op s :disj) s ks)
@@ -2782,9 +2783,9 @@
     "init-proxy" core-init-proxy
     "get-proxy-class" core-get-proxy-class
     # Bit operations
-    "bit-and" core-bit-and
-    "bit-or" core-bit-or
-    "bit-xor" core-bit-xor
+    "__bit-and" core-bit-and
+    "__bit-or" core-bit-or
+    "__bit-xor" core-bit-xor
     "bit-not" core-bit-not
     "bit-shift-left" core-bit-shift-left
     "bit-shift-right" core-bit-shift-right
@@ -2792,7 +2793,7 @@
     "bit-set" core-bit-set
     "bit-flip" core-bit-flip
     "bit-test" core-bit-test
-    "bit-and-not" core-bit-and-not
+    "__bit-and-not" core-bit-and-not
     "unsigned-bit-shift-right" core-unsigned-bit-shift-right
     # Integer coercion / unchecked math
     "int" core-int

src/jolt/evaluator.janet

@@ -1531,10 +1531,14 @@
                (set result (eval-form ctx bindings (in form i)))
                (++ i)))
            result)
-    "if" (let [test-val (eval-form ctx bindings (in form 1))]
-           (if (and (not (nil? test-val)) (not (= false test-val)))
-             (eval-form ctx bindings (in form 2))
-             (if (> (length form) 3) (eval-form ctx bindings (in form 3)) nil)))
+    "if" (do
+           # 2 or 3 argument forms only (spec 03-special-forms X1)
+           (when (or (< (length form) 3) (> (length form) 4))
+             (error (string "Wrong number of args (" (dec (length form)) ") passed to: if")))
+           (let [test-val (eval-form ctx bindings (in form 1))]
+             (if (and (not (nil? test-val)) (not (= false test-val)))
+               (eval-form ctx bindings (in form 2))
+               (if (> (length form) 3) (eval-form ctx bindings (in form 3)) nil))))
     "def" (let [raw-name (in form 1)
                 name-sym (unwrap-meta-name raw-name)
                 # Metadata on the name: keyword/type-hint metadata rides on the