mk: numbero / stringo / symbolo type predicates

Ground-only type tests via project. Each succeeds iff its argument
walks to the corresponding host value type. Composes with membero for
type-filtered enumeration:

  (fresh (x) (membero x (list 1 "a" 2 "b" 3)) (numbero x) (== q x))
    -> (1 2 3)

12 new tests, 328/328 cumulative. Caveat: SX keywords are strings, so
(stringo :k) succeeds.

lib/minikanren/tests/types.sx

@@ -0,0 +1,52 @@
+;; lib/minikanren/tests/types.sx — type-predicate goals.
+
+(mk-test
+  "numbero-on-int"
+  (run* q (numbero 5))
+  (list (make-symbol "_.0")))
+(mk-test "numbero-on-string" (run* q (numbero "5")) (list))
+(mk-test "numbero-on-symbol" (run* q (numbero (quote x))) (list))
+(mk-test "numbero-on-list" (run* q (numbero (list 1))) (list))
+
+(mk-test
+  "stringo-on-string"
+  (run* q (stringo "hi"))
+  (list (make-symbol "_.0")))
+(mk-test "stringo-on-int" (run* q (stringo 5)) (list))
+(mk-test
+  "stringo-on-keyword"
+  (run* q (stringo :k))
+  (list (make-symbol "_.0")))  ;; SX keywords ARE strings
+
+(mk-test
+  "symbolo-on-symbol"
+  (run* q (symbolo (quote x)))
+  (list (make-symbol "_.0")))
+(mk-test "symbolo-on-string" (run* q (symbolo "x")) (list))
+(mk-test "symbolo-on-int" (run* q (symbolo 5)) (list))
+
+;; --- combine with membero for type-filtered enumeration ---
+
+(mk-test
+  "membero-numbero-filter"
+  (run*
+    q
+    (fresh
+      (x)
+      (membero x (list 1 "a" 2 "b" 3))
+      (numbero x)
+      (== q x)))
+  (list 1 2 3))
+
+(mk-test
+  "membero-stringo-filter"
+  (run*
+    q
+    (fresh
+      (x)
+      (membero x (list 1 "a" 2 "b" 3))
+      (stringo x)
+      (== q x)))
+  (list "a" "b"))
+
+(mk-tests-run!)