Expose dataset/conversion scripts as uv entry points

scripts/ is now a proper package (scripts/__init__.py, added to the wheel's
packages), with each script registered under [project.scripts] using its
bare dashed name (e.g. `uv run migrate-geant-steps`). Tests now import these
modules normally instead of loading them by file path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_create_root_files.py

@@ -1,17 +1,10 @@
-import importlib.util
 import json
 import stat
 from pathlib import Path
 
 import pytest
 
-# scripts/ is not an installed package — load the module straight from its path.
-_SPEC = importlib.util.spec_from_file_location(
-    "create_root_files",
-    Path(__file__).resolve().parents[1] / "scripts" / "create_root_files.py",
-)
-create_root_files = importlib.util.module_from_spec(_SPEC)
-_SPEC.loader.exec_module(create_root_files)
+from scripts import create_root_files
 
 parse_detector_spec = create_root_files.parse_detector_spec
 next_shard_index = create_root_files.next_shard_index