Add LECO training script and associated tests

- Implemented `sdxl_train_leco.py` for training with LECO prompts, including argument parsing, model setup, training loop, and weight saving functionality.
- Created unit tests for `load_prompt_settings` in `test_leco_train_util.py` to validate loading of prompt configurations in both original and slider formats.
- Added basic syntax tests for `train_leco.py` and `sdxl_train_leco.py` to ensure modules are importable.

tests/library/test_leco_train_util.py

@@ -0,0 +1,71 @@
+from pathlib import Path
+
+from library.leco_train_util import load_prompt_settings
+
+
+def test_load_prompt_settings_with_original_format(tmp_path: Path):
+    prompt_file = tmp_path / "prompts.yaml"
+    prompt_file.write_text(
+        """
+- target: "van gogh"
+  guidance_scale: 1.5
+  resolution: 512
+""".strip(),
+        encoding="utf-8",
+    )
+
+    prompts = load_prompt_settings(prompt_file)
+
+    assert len(prompts) == 1
+    assert prompts[0].target == "van gogh"
+    assert prompts[0].positive == "van gogh"
+    assert prompts[0].unconditional == ""
+    assert prompts[0].neutral == ""
+    assert prompts[0].action == "erase"
+    assert prompts[0].guidance_scale == 1.5
+
+
+def test_load_prompt_settings_with_slider_targets(tmp_path: Path):
+    prompt_file = tmp_path / "slider.yaml"
+    prompt_file.write_text(
+        """
+targets:
+  - target_class: ""
+    positive: "high detail"
+    negative: "low detail"
+    multiplier: 1.25
+    weight: 0.5
+guidance_scale: 2.0
+resolution: 768
+neutral: ""
+""".strip(),
+        encoding="utf-8",
+    )
+
+    prompts = load_prompt_settings(prompt_file)
+
+    assert len(prompts) == 4
+
+    first = prompts[0]
+    second = prompts[1]
+    third = prompts[2]
+    fourth = prompts[3]
+
+    assert first.target == ""
+    assert first.positive == "low detail"
+    assert first.unconditional == "high detail"
+    assert first.action == "erase"
+    assert first.multiplier == 1.25
+    assert first.weight == 0.5
+    assert first.get_resolution() == (768, 768)
+
+    assert second.positive == "high detail"
+    assert second.unconditional == "low detail"
+    assert second.action == "enhance"
+    assert second.multiplier == 1.25
+
+    assert third.action == "erase"
+    assert third.multiplier == -1.25
+
+    assert fourth.action == "enhance"
+    assert fourth.multiplier == -1.25

tests/test_sdxl_train_leco.py

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+import sdxl_train_leco
+
+
+def test_syntax():
+    assert sdxl_train_leco is not None

tests/test_train_leco.py

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+import train_leco
+
+
+def test_syntax():
+    assert train_leco is not None