'ww test' gains the istest build path (-T injection in build_one/
buildone) and do_test/dotest accept -I, mirroring do_run - both twins.
The 35 converted lib tests drop their interim bare mains (-T
synthesizes the entry from @test fns and rejects a user main); their
35 C run-drivers flip 'ww run' -> 'ww test'; 989_lib_byteid compiles
lib tests under -T (8 user-main probe fixtures stay non-T, gated on
the fixture field). Abort-on-first-failure stands until the deferred
record-and-continue harness lands with the multi-package arc.
Closes the coverage gap that hid task #22's pointer-rooted N_DOT bug:
test/wcc/900_stdlib.c claimed "Coverage lives at lib/bufio/bufiotest.ww"
but no test/wcc/*.c ran bufiotest. New 998_bufio_run runs it and
propagates exit; matches 910_at_test pattern.
