refactor: 清理测试文件和2019相关代码

- 删除测试脚本: test_2026_classification.py, test_lagllama.py, test_timesfm.py, test_ttm.py
- 删除2019相关文件: analyze_2019_*, apply_2019_*, dlinear_2019_*, three_models_2019_*
- 添加集成模型相关代码和分析脚本
- 添加N-BEATS模型和CatBoost分类模型

models/checkpoints/nbeats_btc_1h/metrics.json

@@ -0,0 +1,7 @@
+{
+  "price_mae": 434.07877457530066,
+  "price_rmse": 633.7116744507372,
+  "price_mape": 0.4112793819634811,
+  "direction_accuracy": 0.5083031112807788,
+  "best_val_loss": 0.00040675073481596463
+}