Mirror ref/hare/time's impl layout in the test siblings: constants ->
duration_test.ww (ref/hare/time/duration.ha:9-18 owns the constants);
now/sleep rows -> instant_test.ww (instant is the subject type,
ref/hare/time/instant.ha; now/sleep bodies live in
ref/hare/time/+linux/functions.ha, a platform split ww does not have);
add/diff/compare rows -> arithm_test.ww (ref/hare/time/arithm.ha).
Pure move: every @test block is byte-identical; only the section
banner lines are deleted (the file names now carry them). The stale
file header naming the retired `ww run lib/time/timetest.ww` entry
point is dropped, not relocated (rule 8: it described a WHAT that no
longer exists).
Consumers: Makefile LIBRARY_TESTS entry replaced in place;
test/byteid roster 44->46 (+2).
