Support scanning a specific branch of a table

### Feature Request / Improvement

As far as I can tell, PyIceberg does not directly support being able to scan a particular branch of an iceberg table. For example, there is no way to be able to run an equivalent of queries like

SELECT * FROM `..;`

as documented in https://iceberg.apache.org/docs/1.8.0/branching/#schema-selection-with-branches-and-tags

I can see that PR #941 to add support to _write_ to branches in Pyiceberg is well on its way to be being merged in, so this would be a useful complement.

Alternatively, perhaps I'm mistaken and there is already a way to do this, but it wasn't clear in the documentation

首先阅读 issue 中链接的 Iceberg 分支和 schema 选择文档，然后查看 PR #941，了解现有的分支写入支持。检查当前的 PyIceberg 扫描 API，并确定应如何选择指定分支的表；完成的标准是调用方可以像文档中的查询示例一样扫描表的特定分支。

由索引模型根据 Issue 内容生成。