[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!

Beginne damit, die Verarbeitung von Löschvektoren durch include/paimon/defs.h und DeletionVector::Read nachzuverfolgen, und untersuche anschließend den Lese-/Schreibpfad von BitmapDeletionVector und RoaringBitmap32. Vergleiche das bestehende Verhalten von bitmap32 mit der Magic Number von bitmap64 und den im Issue beschriebenen Java-Paimon-Eigenschaften. Die Aufgabe ist abgeschlossen, wenn Paimon C++ von Java erzeugte bitmap64-Löschvektoren lesen und Iceberg-kompatible erzeugen kann.

Vom Indexierungsmodell aus dem Issue-Text verfasst.