fix: HashTable.all() skips entries keyed 0n

[ejtriple]

Linkable.key defaults to 0n, but all()/findnext used key === 0n as the bucket-sentinel marker. So a real entry keyed 0n — and anything inserted behind it in the same bucket — was skipped by all(), even though find() (which terminates on sentinel identity) still returned it.

const t = new HashTable(8);
t.add(0n, a); t.add(8n, b);   // both hash to bucket 0
[...t.all()]                  // [] — misses both
t.find(0n) === a              // true

Fix: iterate all() by sentinel identity like find() already does, and drop the now-unused findnext. 0n becomes a valid key.

[ejtriple]

Closing - Probably need to revisit IPv6 handling instead of this approach. Now two people (with different ips) will be mapped to the same player, which is no bueno.