Implement Content Stats integration in v4 reader

### Feature Request / Improvement

We recently [implemented](https://github.com/apache/iceberg/pull/16958) the v4 reader. We need to add content stats integration to it

### Query engine

None

### Willingness to contribute

- [x] I can contribute this improvement/feature independently
- [ ] I would be willing to contribute this improvement/feature with guidance from the Iceberg community
- [ ] I cannot contribute this improvement/feature at this time

### Query engine
None

Start by reviewing the v4 reader implementation introduced in PR #16958, then trace how content stats are handled by other readers. Identify the reader entry points and related tests before determining the integration scope. Done means the v4 reader exposes content stats consistently with the existing reader behavior and its tests pass.

Written by the indexing model from the issue text.