fix(examples) Update XGBoost quick-start example for independent object instantiation

[yan-gao-GY]

Issue

Description

The xgboost-quickstart example instantiates xgb object at the first round and persist over FL rounds. This is ok for long-running clients in deployment mode within cross-silo settings. However, it is not feasible to use Flower Simulation and migrate to Flower Next.

Proposal

Implement the same Xgb client as the comprehensive xgb example does, where the xgb object is instantiated independently every single round. No need to persist the xgb object over FL rounds.

Changelog entry

[chongshenng]

Overall looks fine, thanks @yan-gao-GY. I think one more PR is needed to convert this fully to use ClientApp and ServerApp. (We should place start_client and start_server within a if __name__ == "__main__" for this). Let's draft another PR for this upgrade.

You'll also need to update the PR title to conform to the new format. I think something like fix(examples) Update XGBoost quickstart examples for independent object instantiation could work.

[yan-gao-GY]

@chongshenng Thanks a lot for your comments and suggestions!

Do we want to fully replace start_client and start_server now? I saw other examples keep both and using Flower Next with a preview label.

[jafermarq]

@chongshenng Thanks a lot for your comments and suggestions!

Do we want to fully replace start_client and start_server now? I saw other examples keep both and using Flower Next with a preview label.

Let's do that later in a different PR.

[chongshenng]

@chongshenng Thanks a lot for your comments and suggestions!
Do we want to fully replace start_client and start_server now? I saw other examples keep both and using Flower Next with a preview label.

Let's do that later in a different PR.

Agreed.

[chongshenng]

lgtm!