One durable runtime journal entry.
Entries are intentionally shaped as append-only facts. Checkpoints and live wakeups are derived from replaying entries; they are not the source of truth.
@type t() :: %SquidMesh.Runtime.DispatchProtocol.Entry{ data: map(), occurred_at: DateTime.t(), thread: thread(), type: atom() }
@type thread() :: {:run, String.t()} | {:dispatch, String.t()} | {:run_index, String.t()}