Add branch merge strategies

### Feature Request / Improvement

Add merge strategies commonly used in version control systems to pyiceberg. Motivated by some of the discussion found here https://github.com/apache/iceberg-python/issues/2428:

1. **MERGE**: creating a merge commit that preserves history of both branches
2. **SQUASH**: condenses all commits from source branch into a single clean commit on target branch
3. **REBASE**: creates linear history by replaying commits from source branch on top of target branch
4. **CHERRY_PICK**: selects and applies specific individual commits from one branch to another
5. **FAST_FORWARD**: moves target branch pointer forward when no divergent commits exist (no merge commit needed)

El issue no menciona archivos, tests ni puntos de entrada. Empieza leyendo la discusión enlazada en el issue 2428 para determinar la API y el alcance previstos; después, localiza las operaciones de ramas y los tests existentes de PyIceberg. Se considera terminado cuando se hayan acordado y se admitan las cinco estrategias enumeradas.

Escrito por el modelo de indexación a partir del texto del issue.