iyi 0.7.0

The language owns a collector, and it runs itself.

Behind -Dgc_iyi, the whole machine: a size-class arena allocator that
costs no symbol and no library, roots from the stack, the spilled
registers, the globals and every suspended fiber's stack, marking that
is precise where the header names a type and conservative everywhere
else, a sweep that hands memory back, and an allocation-pressure
trigger — one collection per live-set of garbage, floored at a MiB,
with nobody calling collect. Every stage is gated, every gate proves
it can fail, and all of them run in CI.

What it is not, said here rather than found: opt-in — the default
build still allocates and never frees, and moving that default is
0.8.0's measurement, not this release's side effect. Collections run
on the allocating fiber at allocation points only; arenas stay mapped
for their free lists; finalizers and weak references wait on the
language having the features; threads, and with them parallel
marking, wait on threads.

And a fix every released compiler needed: the prelude's own memset
strode eight elements where it meant eight bytes, so every
runtime-sized clear left seven of eight bytes dirty and wrote one
word in eight far past its count. Invisible on the bump allocator's
zero tail, consistent with everything the Windows watch ever
recorded, fixed on all three targets that carried it.

.iyimod format is v43 — the Layouts section carries each type's
pointer map — so a 0.6.0 artifact is rejected by a 0.7.0 build and
rebuilt, never migrated. Both tarballs below were built and proven by
the tagged run itself.

Extract, put bin on PATH: iyi run, iyi lsp, iyi check — nothing to
configure.