wwtest: native package-test coordinator

Single-directory package-test planner: discovers *.ww, groups white-box
and external <pkg>_test sources, composes the combined test package,
builds it through the sibling ww driver, and runs it with the runtime's
-package/-list/-timeout-ms contract. test/package holds its E2E corpus
and the manual runtime fixture set.

test/package/routing/a_helper_test.ww

@@ -0,0 +1,5 @@
+package routing;
+
+// Canonical test-only helper: no @test declaration in this file.  Both
+// same-package test files below share it through the single white-box build.
+fn privatevalue() int = { return value() + 1; };

test/package/routing/b_white_test.ww

@@ -0,0 +1,5 @@
+package routing;
+
+@test fn private_helper_first() void = {
+	assert(privatevalue() == 8);
+};

test/package/routing/external_test.ww

@@ -0,0 +1,7 @@
+package routing_test;
+
+import routing;
+
+@test fn external_package() void = {
+	assert(routing.value() == 7);
+};

test/package/routing/routing.ww

@@ -0,0 +1,3 @@
+package routing;
+
+export fn value() int = { return 7; };

test/package/routing/routing_test.ww

@@ -0,0 +1,6 @@
+package routing;
+
+@test fn same_package() void = {
+	assert(value() == 7);
+	assert(privatevalue() == 8);
+};