Remove XGB stuff moved to Eventdisplay-ML

[GernotMaier]

move to https://github.com/Eventdisplay/Eventdisplay-ML

[Copilot]

Pull request overview

This PR removes XGBoost-related Python code and dependencies that have been migrated to the separate Eventdisplay-ML repository. The removal includes training and inference scripts, supporting utilities, tests, and the Python environment configuration.

Key changes:

• Removes XGBoost direction reconstruction training and inference implementations
• Removes Python-specific environment configuration
• Removes associated test files

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
py/training_variables.py	Removes XGBoost training variable definitions used for direction reconstruction
py/trainXGBoostforDirection.py	Removes XGBoost model training script (437 lines) for multi-target direction BDTs
py/applyXGBoostforDirection.py	Removes XGBoost model inference script (492 lines) for direction reconstruction
py/tests/test_applyXGBoostforDirection.py	Removes unit tests for XGBoost inference functionality
environment.yml	Removes conda environment specification with Python 3.13 and ML dependencies

Note: While the code removal is clean, there are references to this XGBoost functionality remaining in the repository that are not addressed in this PR:

1. docs/changes/322.feature.md documents the XGBoost feature that is now being removed
2. pytest.ini references a "python" directory that may no longer exist
3. No documentation update explaining the migration to Eventdisplay-ML or linking to the new repository

These items should be addressed in a follow-up PR or included in this one to maintain documentation consistency.

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