Adding week partition transform

### Feature Request / Improvement

We have multiple partition transformations like day, month, year, hour.... but not `week` which sometimes is interesting

### Query engine

None

### Willingness to contribute

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

Start by reading the existing day, month, year, and hour partition transformations to find where a week transform belongs. Trace how those transforms are represented and exposed, then add week consistently and verify that partitioning by week works as expected. Ask the Iceberg community for guidance on the intended week semantics if the existing code does not make them clear.

Written by the indexing model from the issue text.