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/clojure-for-test.janet

@@ -1,35 +0,0 @@
-# Ported from clojure/test_clojure/for.clj
-(use ../src/jolt/api)
-(defn ct-eval [ctx s] (normalize-pvecs (eval-string ctx s)))
-
-(print "Ported For Tests")
-
-# --- When ---
-(print "test-for :when...")
-(let [ctx (init)]
-  (assert (= true (ct-eval ctx
-    "(= (for [x (range 10) :when (odd? x)] x)
-        (quote (1 3 5 7 9)))")) "for :when odd?")
-  (assert (= true (ct-eval ctx
-    "(= (for [x (range 4) y (range 4) :when (odd? y)] [x y])
-        (quote ([0 1] [0 3] [1 1] [1 3] [2 1] [2 3] [3 1] [3 3])))")) "for nested :when"))
-(print "  ok")
-
-# --- Let ---
-(print "test-for :let...")
-(let [ctx (init)]
-  (assert (= true (ct-eval ctx
-    "(= (for [x (range 3) y (range 3) :let [z (+ x y)] :when (odd? z)] [x y z])
-        (quote ([0 1 1] [1 0 1] [1 2 3] [2 1 3])))")) "for :let :when"))
-(print "  ok")
-
-# --- Nesting ---
-(print "test-for nesting...")
-(let [ctx (init)]
-  (assert (= true (ct-eval ctx
-    "(= (for [x (quote (a b)) y (interpose x (quote (1 2))) z (list x y)] [x y z])
-        (quote ([a 1 a] [a 1 1] [a a a] [a a a] [a 2 a] [a 2 2]
-                [b 1 b] [b 1 1] [b b b] [b b b] [b 2 b] [b 2 2])))")) "for nested interpose"))
-(print "  ok")
-
-(print "\nAll Ported For tests passed!")