lib/time+test: add types, ops, now

Replaces the lib/time placeholder (a monotonic(*timespec) shim that
predated lib/os's syscall surface). Ships Hare's time module first
cut per ref/hare/time/{duration,instant,arithm,+linux/functions}.ha:

- duration (i64 ns); nanosecond / microsecond / millisecond / second
  constants.
- instant (sec, nsec) — Hare's layout, NOT POSIX's nsec:u32. Matches
  Linux struct timespec on 64-bit, so &instant lands directly in
  clock_gettime.
- clock enum: realtime + monotonic only. The rest of Hare's set
  (process_cpu / thread_cpu / boot / realtime_alarm / boot_alarm / tai)
  graduates when a caller actually needs it (rule 9).
- now(c: clock) instant — aborts on EINVAL/EFAULT (mirrors Hare's
  abort-on-impossible-errno). Deliberately NOT (instant | oserror) to
  sidestep task #9's 1-word-payload tagged-return trap.
- add / diff / compare on instants per ref/hare/time/arithm.ha
  verbatim.

Deferred to follow-up commits when a caller surfaces: sleep, format /
strftime, time.chrono / time.date calendar, timezone, time.error
sum-return shape, time.unix helpers, time.mult, conversion helpers.

Tests at lib/time/timetest.ww (15 rows, table-pattern, semantic per
Class B doctrine). Driver test/wcc/977_time_run.c slotted between
976_stat_run and 978_intdiv_signed in the 9xx _run band.
examples/cmatrix migrates to the new API in the same commit (sole
pre-existing caller — bisect-clean per rule 11).

Class B bug #16 (sign-extend before IDIVQ) was surfaced by the
negative-duration rows during this work; landed 63332fe..4fa4bcf
before this commit. Rows 8-9 (addneg_noborrow / addneg_borrow) are
the load-bearing Class B exercisers; would have stayed silently wrong
pre-#16.

lib/time's own .s output has a cstage/wwstage label-counter skew in
add (cstage emits add_ct_7/_ce_8/_end_6 vs wwstage _6/_7/_5). Filed
as task #15; non-bootstrap-blocking since lib/time is outside the
selfhost toolchain transitive chain.

Makefile

@@ -252,7 +252,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_dyn_ww $(BIN)/test_selfcheck $(BIN)/test_at_test_ww \
 	  $(BIN)/test_fmt_run $(BIN)/test_log_run $(BIN)/test_fnmatch_run \
 	  $(BIN)/test_shlex_run $(BIN)/test_getenv_run $(BIN)/test_dirs_run \
-	  $(BIN)/test_stat_run \
+	  $(BIN)/test_stat_run $(BIN)/test_time_run \
 	  $(BIN)/test_intdiv_signed \
 	  $(BIN)/test_memio_run $(BIN)/test_temp_run $(BIN)/test_getopt_run \
 	  $(BIN)/test_base32_run $(BIN)/test_base64_run \
@@ -585,6 +585,10 @@ $(BIN)/test_stat_run: test/wcc/976_stat_run.c $(BIN)/ww $(BIN)/w6c \
 		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_time_run: test/wcc/977_time_run.c $(BIN)/ww $(BIN)/w6c \
+		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_intdiv_signed: test/wcc/978_intdiv_signed.c $(BIN)/ww $(BIN)/w6c \
 		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<