Support Concurrency Safety Validation: Implement `validateAddedDataFiles`

[sungwy]

There's been a lot of continued interest in using multiple PyIceberg applications concurrently and having proper support for optimistic concurrency.

I think the best place to start is through the implementation of the individual validation functions

This subtask tracks the implementation of validateAddedDataFiles function.

Java Reference

[kaushiksrini]

hey @sungwy, i can take a look at this!