The server's signer set, pre-normalized to x-only hex for cheap repeated
lookups. Built once per migration/reporting pass from a fresh
ArkInfo snapshot via signerSetFromInfo.
Deprecated signers keyed by x-only hex, mapped to their cutoff. The cutoff
is always a bigint (arkd advertises it non-nullable); 0n means "no cutoff
advertised" (→ DUE_NOW).
The server's signer set, pre-normalized to x-only hex for cheap repeated lookups. Built once per migration/reporting pass from a fresh ArkInfo snapshot via signerSetFromInfo.