test: restructure into unit / integration / spec layers + shared harness

Reorganize the flat 49-file test/ into three layers (jpm test recurses, so all
are still discovered):
- test/unit/        white-box component tests (reader, evaluator, types,
                    persistent-map, lazy-seq, macro, interop, compiler)
- test/integration/ cross-cutting + regression batteries (conformance, jank,
                    sci-bootstrap/runtime, features, systematic-coverage, api,
                    core, namespaces, ported clojure suites) and
   .../ports/       ported clojure/cljs test batches pending consolidation
- test/spec/        the behavioral contract (built out in following commits)
- test/support/harness.janet  shared defspec table runner (cases compared via
                    Jolt's own =, with a :throws sentinel) + expect= helpers

Files moved with git mv (history preserved) and import paths fixed for depth.
jpm test green. README Test section updated.

Next: build out test/spec/ to cover the public API area-by-area, mining the
integration batteries and filling gaps.

test/integration/namespace-test.janet

@@ -0,0 +1,92 @@
+(use ../../src/jolt/reader)
+(use ../../src/jolt/types)
+(use ../../src/jolt/evaluator)
+
+# Helper: parse and eval in a fresh ctx
+(defn eval-str [s]
+  (let [ctx (make-ctx)
+        form (parse-string s)]
+    (eval-form ctx @{} form)))
+
+(print "1: in-ns...")
+(let [ctx (make-ctx)]
+  (def form (parse-string "(in-ns my.app)"))
+  (eval-form ctx @{} form)
+  (assert (= "my.app" (ctx-current-ns ctx)) "in-ns switches namespace"))
+(print "  passed")
+
+(print "2: def in different namespace...")
+(let [ctx (make-ctx)]
+  (eval-form ctx @{} (parse-string "(in-ns my.app)"))
+  (eval-form ctx @{} (parse-string "(def x 42)"))
+  (let [ns (ctx-find-ns ctx "my.app")
+        v (ns-find ns "x")]
+    (assert (= 42 (var-get v)) "def works in new namespace")))
+(print "  passed")
+
+(print "3: ns form...")
+(let [ctx (make-ctx)]
+  (eval-form ctx @{} (parse-string "(ns my.lib)"))
+  (assert (= "my.lib" (ctx-current-ns ctx)) "ns sets current namespace"))
+(print "  passed")
+
+(print "4: ns with require...")
+(let [ctx (make-ctx)]
+  # Set up a namespace with some vars
+  (let [other-ns (ctx-find-ns ctx "other.lib")]
+    (ns-intern other-ns "f" (fn [x] (inc x))))
+  # Now ns with require
+  (eval-form ctx @{} (parse-string "(ns my.app (:require [other.lib :as o]))"))
+  # current-ns should be my.app
+  (assert (= "my.app" (ctx-current-ns ctx)) "ns with require sets current namespace")
+  # Alias should be registered
+  (let [ns (ctx-find-ns ctx "my.app")
+        aliased (ns-import-lookup ns "o")]
+    (assert (= "other.lib" aliased) "alias o -> other.lib registered")))
+(print "  passed")
+
+(print "5: require form (standalone)...")
+(let [ctx (make-ctx)]
+  (eval-form ctx @{} (parse-string "(require '[other.lib :as o])"))
+  (let [ns (ctx-find-ns ctx "user")
+        aliased (ns-import-lookup ns "o")]
+    (assert (= "other.lib" aliased) "standalone require registers alias")))
+(print "  passed")
+
+(print "6: qualified symbol via alias...")
+(let [ctx (make-ctx)]
+  # Set up target ns
+  (let [target (ctx-find-ns ctx "other.lib")]
+    (ns-intern target "f" (fn [x] (inc x))))
+  # Register alias
+  (let [ns (ctx-find-ns ctx "user")]
+    (ns-import ns "o" "other.lib"))
+  # Resolve o/f and call it
+  (let [form (parse-string "(o/f 41)")
+        result (eval-form ctx @{} form)]
+    (assert (= 42 result) "qualified call via alias works")))
+(print "  passed")
+
+(print "7: require then use alias...")
+(let [ctx (make-ctx)]
+  # Set up target ns
+  (let [target (ctx-find-ns ctx "math.lib")]
+    (ns-intern target "add" (fn [a b] (+ a b))))
+  # require + use
+  (eval-form ctx @{} (parse-string "(require '[math.lib :as m])"))
+  (let [result (eval-form ctx @{} (parse-string "(m/add 1 2)"))]
+    (assert (= 3 result) "require + alias + call chain works")))
+(print "  passed")
+
+(print "8: ns form requires multiple...")
+(let [ctx (make-ctx)]
+  (let [ns1 (ctx-find-ns ctx "a.lib")]
+    (ns-intern ns1 "f" (fn [x] (inc x))))
+  (let [ns2 (ctx-find-ns ctx "b.lib")]
+    (ns-intern ns2 "g" (fn [x] (dec x))))
+  (eval-form ctx @{} (parse-string "(ns user (:require [a.lib :as a] [b.lib :as b]))"))
+  (assert (= 43 (eval-form ctx @{} (parse-string "(a/f 42)"))) "alias a works")
+  (assert (= 41 (eval-form ctx @{} (parse-string "(b/g 42)"))) "alias b works"))
+(print "  passed")
+
+(print "\nAll namespace tests passed!")