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/arrnarrow_struct_over/case.ww

@@ -0,0 +1,7 @@
+//ww:error "array element out of range"
+// #251 carrier: out-of-range element at a struct-field init (was a ww
+// over-accept). From test/wcc/951_arrlit_elem_narrow_run.c struct_over.
+package main;
+type enc = struct { m: [2]u8 };
+let E: enc = enc { m = [300, 1] };
+export fn main() i32 = { return E.m[0]: i32; };