lib: migrate every test file to the canonical *_test.ww name

25 renames (git mv, content untouched). _test.ww is what the package
coordinator's test detection and the sep loader's canonical exclusion
key on; the old *test.ww spellings survived only through the
line-leading-@test compatibility scan. Consumers updated in place:
LIBRARY_TESTS, the libbyteid roster, the 901/974/975/976 carriers that
copy or invoke these files, and the check.c/check.ww + path/ftos
comments that cite them. Closes the open-driver-work migration bullet.

docs/test-system-v2.md

@@ -310,9 +310,6 @@ drift:
   single-threaded by design today).
 - A package-level `-o` contract (single-file `ww test -o` exists; directory
   packages publish fixed `<package>.test` stems under `-c`).
-- Universal `*_test.ww` filename migration for library tests (several
-  library suites still use the older `*test.ww` names, enumerated by
-  `LIBRARY_TESTS` and the `989_lib_byteid` roster).
 - The remaining invalid-`@test` attribute-shape diagnostics (exported
   tests, prototypes, arguments, variadics, non-void returns, duplicate
   annotations) with stable text in both frontends.