V3 Tracking issue

Tracks the progress of the V3 implementation

- [ ] New DataTypes
- [x] **UnknownType**: Added in https://github.com/apache/iceberg-python/pull/1681
- [x] **Timestamp(Tz)NanoType**: Introduced in https://github.com/apache/iceberg-python/pull/1632
- [ ] **VariantType**: https://github.com/apache/iceberg-python/issues/1819
- [ ] **Geometry**/**Geography**: https://github.com/apache/iceberg-python/issues/1820
- [ ] Default value:
- [x] https://github.com/apache/iceberg-python/issues/1836 / https://github.com/apache/iceberg-python/pull/1644
- [x] https://github.com/apache/iceberg-python/pull/1770
- [x] Prerequisite: https://github.com/apache/iceberg-python/pull/1805
- [x] Multi-arg transforms
- Reading of the metadata has been added in https://github.com/apache/iceberg-python/pull/1554
- Supporting multi-arg transforms still needs to happen
- [x] Row-level lineage
- https://github.com/apache/iceberg-python/issues/1821
- [ ] Deletion vectors
- [x] Read support is being added in https://github.com/apache/iceberg-python/pull/1516
- [ ] Write support

首先查看与 VariantType、Geometry/Geography、row-level lineage、multi-argument transforms 和 deletion-vector write support 相关的已链接 V3 子 issue 和 pull request。只有在每个未勾选的 V3 检查清单项都已完成，且其链接的工作已解决后，跟踪 issue 才算完成。

由索引模型根据 Issue 内容生成。