[Announcement] Repository sealed and development moved to Apache Paimon C++

### Search before asking

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

### Motivation

This repository has completed its mission as the original home of Paimon C++.

We have contributed all functionality from this repository to
[apache/paimon-cpp](https://github.com/apache/paimon-cpp), which is now the official C++
implementation of Apache Paimon. The official repository provides the same functionality and APIs
as this repository.

To avoid splitting development and community contributions across multiple repositories, this
repository is now sealed.

### Solution

All future development and community activity should move to the official Apache repository:

- Use [apache/paimon-cpp](https://github.com/apache/paimon-cpp) for Paimon C++.
- Submit all new issues and feature requests to the official repository.
- Submit all future pull requests and code contributions to the official repository.
- Authors of currently open pull requests are welcome to resubmit their changes to the official
repository.

New features, bug fixes, and other changes will no longer be merged into this repository.

### Anything else?

Thank you to everyone who has used, contributed to, and supported this project. We look forward to
continuing the development of Paimon C++ together in the Apache community.

### Are you willing to submit a PR?

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

This repository is sealed, and development has moved to apache/paimon-cpp. Do not start work here; submit future issues, pull requests, and contributions to the official Apache repository instead.

Written by the indexing model from the issue text.