[Feature] Support 64-bit deletion vectors in Paimon C++

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/paimon-cpp/issues) and found nothing similar.

### Motivation

### Motivation

Java Paimon supports both 32-bit and 64-bit deletion vectors through:

```properties
deletion-vectors.enabled=true
deletion-vectors.bitmap64=true

Paimon C++ currently exposes the deletion-vectors.bitmap64 option, but bitmap64 deletion vectors are not implemented:
- include/paimon/defs.h marks bitmap64 DV as unsupported.
- DeletionVector::Read recognizes the bitmap64 magic number but returns NotImplemented.
- Only BitmapDeletionVector, backed by RoaringBitmap32, is currently used for deletion-vector reads and writes.
As a result, Paimon C++ cannot read tables containing bitmap64 deletion vectors produced by Java Paimon, and cannot produce Iceberg-compatible deletion vectors.

### Solution

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!

首先透過 include/paimon/defs.h 和 DeletionVector::Read 追蹤刪除向量的處理，接著檢查 BitmapDeletionVector 和 RoaringBitmap32 的讀寫路徑。將現有的 bitmap32 行為與 bitmap64 的 magic number 以及 issue 中描述的 Java Paimon 屬性進行比較。當 Paimon C++ 可以讀取 Java 產生的 bitmap64 刪除向量，並產生與 Iceberg 相容的刪除向量時，即表示完成。

由索引模型根據 Issue 內容生成。