[feature request] Support cherrypick and fastforward operations

### Feature Request / Improvement

In an effort to support WAP in PyIceberg there is work undergoing for implementing staged snapshots ([issue](https://github.com/apache/iceberg-python/issues/2214)). We would also need to support cherrypicking and fastworward to reference the staged snapshot as the current one.

Start by reading issue 2214 and the staged-snapshots work it describes to understand the current snapshot model and entry points. Define how cherrypick and fast-forward should reference a staged snapshot, then verify the behavior against the agreed snapshot semantics; the issue does not name specific files or tests.

Written by the indexing model from the issue text.