refactor: split Store into StreamStore and RecordStore

- StreamStore: fetch(begin, end, key) for stream access (SEQ/SFT)
- RecordStore: mixin with fetch_record(i, key) for record access
- H5Store/MmapStore/JsonlStore now dual-inherit both (C3 MRO)
- JsonlStore supports lazy mode via processor= (no TokenizeTransform)
- RecordDataset base class holds processor, DPO/GRPO simplified
- dpo_tokenize pure function for on-the-fly JSONL tokenisation
- DatasetFactory builds processor for jsonl+record datasets
- train.py passes tokenizer_path=param_path uniformly
- progress: len(dataset) returns sample count (stream=windows, record=records)
- json no longer auto-detected as jsonl format

scripts/tools/train.py

@@ -460,6 +460,7 @@ def train(
         load_path=data_root_path,
         window_size=window_size,
         stride=stride,
+        tokenizer_path=param_path,
     )
 
     optimizer_fn = partial(