test: parallelize golden suite via ephemeral ports + nextest
The boot-level golden tests each booted a real `leveva` on a fixed port,
forcing a global lock that serialized the whole suite (~230s). Make them
parallel-safe and run them under nextest:
- Ephemeral ports: each daemon reserves `127.0.0.1:0`, templates its
fixture to the assigned client/server ports, and threads them through
the clients/peers. Per-port flock + a CPU-count slot semaphore
(MAX_CONCURRENT_DAEMONS=128) bound concurrency.
- `.config/nextest.toml`: a `golden` test-group caps in-flight daemons,
with `retries = 2` and a 30s `slow-timeout terminate-after` backstop.
- Streaming `read_until`: a per-connection `pending` buffer returns
through the sentinel line and retains the rest, and a 30s overall
deadline now PANICS (was a silent hang) so a never-arriving sentinel
fails loudly. Sentinels that previously matched on a since-coalesced
read were re-pointed at their transcript's true last line; a handful
of snapshots reattributed accordingly (content preserved).
- Fakelag off in tests: the daemon arms flood protection unless
`LEVEVA_DISABLE_FAKELAG=1`, which the harness sets by default so
barrier-paced clients don't eat the fakelag *delay*; the dedicated
flood goldens opt back in via `want_fakelag()`.
- Slow-test sentinels: `golden_rehash_conf` waited on a `376` its
no-MOTD config never sends (124s -> 1s); `golden_s2s_monitor` keyed
on a too-early `731`.
Suite: ~230s -> ~25s.
Assisted-by: Claude Opus 4.8 via Claude Code
Signed-off-by: Xe Iaso <me@xeiaso.net>