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/ports/phase8-test.janet

@@ -0,0 +1,44 @@
+# Phase 8: Protocol System Tests
+(use ../../../src/jolt/api)
+(defn ct-eval [ctx s] (normalize-pvecs (eval-string ctx s)))
+
+(print "35: defprotocol...")
+(let [ctx (init)]
+  (ct-eval ctx "(defprotocol Greet (greet [this]))")
+  (let [p (ct-eval ctx "Greet")]
+    (assert (not (nil? p)) "protocol var exists")
+    (assert (= :jolt/protocol (get p :jolt/type)) "protocol type tag")
+    (assert (get (get p :methods) :greet) "protocol has greet method"))
+  (assert (or (function? (ct-eval ctx "greet")) (cfunction? (ct-eval ctx "greet"))) "method fn exists"))
+(print "  passed")
+
+(print "36: extend-type...")
+(let [ctx (init)]
+  (ct-eval ctx "(deftype Person [name])")
+  (ct-eval ctx "(defprotocol Namable (get-name [this]))")
+  (ct-eval ctx "(extend-type Person Namable (get-name [this] (.-name this)))")
+  (assert (= "Alice" (ct-eval ctx "(get-name (Person. \"Alice\"))")) "extend-type works"))
+(print "  passed")
+
+(print "37: extend-protocol...")
+(let [ctx (init)]
+  (ct-eval ctx "(deftype Dog [breed])")
+  (ct-eval ctx "(deftype Cat [color])")
+  (ct-eval ctx "(defprotocol Animal (speak [this]))")
+  (ct-eval ctx "(extend-protocol Animal
+    Dog (speak [this] (str \"woof from \" (.-breed this)))
+    Cat (speak [this] (str \"meow from \" (.-color this))))")
+  (assert (= "woof from poodle" (ct-eval ctx "(speak (Dog. \"poodle\"))")) "dog speak")
+  (assert (= "meow from black" (ct-eval ctx "(speak (Cat. \"black\"))")) "cat speak"))
+(print "  passed")
+
+(print "38: satisfies?...")
+(let [ctx (init)]
+  (ct-eval ctx "(deftype Point [x y])")
+  (ct-eval ctx "(defprotocol Locatable (location [this]))")
+  (ct-eval ctx "(extend-type Point Locatable (location [this] [(.-x this) (.-y this)]))")
+  (assert (= true (ct-eval ctx "(satisfies? Locatable (Point. 3 4))")) "satisfies? true")
+  (assert (= false (ct-eval ctx "(satisfies? Locatable {:x 1})")) "satisfies? false"))
+(print "  passed")
+
+(print "\nAll Phase 8 tests passed!")