Base64URL cursor encoding for audit log pagination (D-13).
Format: Base64URL("<inserted_at_usec>|<uuid>") — no padding, no signing.
Cursors carry only timestamp + id, so tampering only shifts the pagination
window; no sensitive data is disclosed.
Summary
Functions
@spec decode(binary() | nil) :: {:ok, {DateTime.t(), binary()}} | {:error, :invalid_cursor}
@spec encode(DateTime.t(), binary()) :: String.t()