Reject decimal numbers with leading zeros
Important when parsing a "checkpoint" (see https://github.com/C2SP/C2SP/blob/main/tlog-checkpoint.md), since leading zeros on the size line affects the signature.
Important when parsing a "checkpoint" (see https://github.com/C2SP/C2SP/blob/main/tlog-checkpoint.md), since leading zeros on the size line affects the signature.