feat: stdlib daily APIs, macro tt/type paste, riscv64 cross smoke

Sessions 83–87: grow Array/Map/String/Test ergonomics; delimiter-balanced
and juxta :tt macros plus $t:type fragments; expression-level $(…),* in
templates; selfhost slice lits; riscv64/aarch64 cross smoke helper and
freestanding docs. Null-safe CBE type names and String_StartsWith.

lib/Test.bux

@@ -46,6 +46,15 @@ module Std::Test {
         }
     }
 
+    /// Assert two strings differ.
+    func Test_AssertNeqString(a: String, b: String) {
+        if String_Eq(a, b) {
+            PrintLine("ASSERT_NEQ_STRING FAILED: both are");
+            PrintLine(b);
+            bux_exit(1);
+        }
+    }
+
     /// Assert two bools are equal.
     func Test_AssertEqBool(a: bool, b: bool) {
         if a != b {