Pluggable Scan Planning

### Feature Request / Improvement

Umbrella issue. Today we have tightly coupled query planning in Python. This works well but runs into limitations when it comes to concurrency and performance. Having pluggable query planning will allow for:

- **Python based query planning** which is working today and is proven.
- **Iceberg-Rust based query planning** as suggeted in https://github.com/apache/iceberg-python/issues/2159#issuecomment-3033339213.
- **REST Catalog server side planning** this leverages the REST Catalog to plan the query, rather than the client. First issue can be found here: https://github.com/apache/iceberg-python/issues/2302.

As an API, I think it makes sense to follow the Server Side planning. So a `PlanTableScanRequest` as an input, and the [ScanTasks](https://github.com/apache/iceberg/blob/68a241615e104d97a86c932c381d7dfac802d769/open-api/rest-catalog-open-api.py#L1290) as the output.

首先阅读这个总 issue，以及 issue 2302；后者涵盖 REST Catalog 首项服务端规划工作。检查提议的 PlanTableScanRequest 输入和 ScanTasks 输出，然后将它们与现有的 Python 查询规划路径进行比较。完成的标准是达成一个一致认可的可插拔规划 API，能够支持 Python、Iceberg-Rust 和 REST Catalog 规划。

由索引模型根据 Issue 内容生成。