test(xmtp_mls): randomized bidi delivery fuzz against the live node

Two seeded fuzz tests run against the containerized backend, closing the
gap the scripted suite cannot: unscripted interleavings, and the real
server rather than a model of it.

- fuzz_server_honors_the_bidi_wave_contract: raw BidiConnection under
  random publish/add/yank/remove churn; asserts always-ack, per-topic
  wave cursor order, the live-lane hold for yanked topics (armed at the
  wave's first tagged frame — stream-ordered, race-free), live frames
  strictly above the cross-lane high-water, and completeness above the
  lowest asked cursor against a final authoritative query.
- fuzz_transport_delivery_never_loses_above_the_floor: a real
  BidiTransport whose wire runs through toxiproxy; random lease/yank/
  unsubscribe/stall/suspend-resume schedules plus real TCP blips; asserts
  per-lease exactly-once above its floor, completeness to the live edge
  for every surviving lease, catch-up liveness, and recovery-chain union
  completeness across backpressure drops (relinked from received state —
  the durable-cursor recovery shape). Welcome topics ride the same
  invariants; schedule telemetry is logged so dark levers are visible.

Seeds print at start and ride every assertion (XMTP_BIDI_FUZZ_SEED to
replay; XMTP_BIDI_FUZZ_ROUNDS to scale). nextest retries are disabled
for these tests — a retry would re-roll the seed and mask a finding.

Already earned its keep: caught the removes-wave/untagged-tombstone
collision and validated the deref-mid-replay fix, both in the tags PR.

Author: tylerhawkes

.config/nextest.toml

@@ -42,3 +42,13 @@ path = "junit.xml"
 platform = 'cfg(all(target_family = "wasm", target_os = "unknown"))'
 default-filter = "not (test(/\\w*commit_log*/))"
 threads-required = 2
+
+# Fuzz tests print their seed and must fail loudly — a retry would re-roll
+# the seed and mask the finding.
+[[profile.default.overrides]]
+filter = 'test(/bidi_fuzz/)'
+retries = 0
+
+[[profile.ci.overrides]]
+filter = 'test(/bidi_fuzz/)'
+retries = 0