This class provides some methods for validating sequence numbers. It provides a method
validateSequenceNumber(String) which validates a sequence number by attempting to get an iterator from
Amazon Kinesis for that sequence number. (e.g. Before checkpointing a client provided sequence number in
RecordProcessorCheckpointer#checkpoint(String) to prevent invalid sequence numbers from being checkpointed,
which could prevent another shard consumer instance from processing the shard later on). This class also provides a
utility function
isDigits(String) which is used to check whether a string is all digits