test: migrate Fam13 misc checker/coercion value tests to @test (#5-C6)

Final fold-2 chunk. The 12 Fam13 single-file value drivers move from
test/wcc/*_run.c into in-language @test row-tables under test/lang/:

- value rows -> test/lang/*_test.ww (12 files)
- reject rows -> runww //ww:error carriers (13, dual-stage non-vacuous)
- nullable abort rows -> runww //ww:run-exit 1 carriers (3)
- 953_globalslice_arg -> _runonly (cs!=ww checker divergence, #28)
- 788 value_not_type_neg + 953_arrlit_slice reject_assign kept as slim
  rc-only .c pins (divergent-diag dual-reject, mutation-gated); 788 #29

Coverage parity verified row-by-row vs each retired driver; advisor-
ratified carve taxonomy; two-round reviewed. Floor ratchet follows.

test/wcc/data/nullable_tryunw_null/case.ww

@@ -0,0 +1,12 @@
+//ww:run-exit 1
+// #15 (F4) carrier: `p!` on a null (*int|void) must ABORT (exit 1), not treat
+// null as success and deref (SEGV pre-fix). Clean twin tryunw_valid in
+// test/lang/nullable_try_test.ww carries the abort-arm byte-id; this pins the
+// runtime abort. Underlying fix was wwstage cgen (cgtryunw nullable arm). From
+// 949_nullable_try_run.c.
+package main;
+fn h(p: (*int|void)) int = { let q = p!; return *q; };
+export fn main() i32 = {
+	let r = h(void);
+	return 50;
+};