fix: gossip stale overwrite + async remember trust/tags

[cursor]

Bug and impact

1. Gossip stale overwrite (data loss)

In distributed deployments using GossipProtocol, delayed gossip events could overwrite newer local memory writes.

Trigger: Node A writes key=state with a recent value. A stale gossip batch arrives from Node B (same key, older value) without ts_ns. receive() called remember() without a timestamp, which stamped wall-clock now() — newer than the local write — and silently replaced the correct value.

2. AsyncHiveStack.remember drops trust/tags (metadata loss / trust bypass)

AsyncHiveStack.remember() accepted trust and tags kwargs but only forwarded key and value to the underlying HiveStack. All async writes stored trust=1.0 and empty tags, breaking min_trust filtering and tag-based retrieval.

Root cause

• Gossip: receive() did not propagate origin ts_ns, defeating RustBrain monotonic timestamp protection.
• Async: run_in_executor(None, self._stack.remember, key, value) omitted keyword args.

Fix and validation

• Gossip: skip updates for existing keys when ts_ns is missing; pass ts_ns when present so TimestampRegression rejects stale writes.
• Async: delegate via lambda that forwards trust and tags.

Tests added:

• test_gossip_without_ts_ns_does_not_overwrite_existing_key
• test_gossip_with_older_ts_ns_is_rejected
• test_gossip_with_newer_ts_ns_updates_existing_key
• test_async_remember_preserves_trust_and_tags

Validation: 180 passed, 8 skipped