refactor : 基于声明式 JSON 配置的预处理管线重构

- 用工厂注册的 MaskBuilder（chat/instruction/text）替换硬编码的 _transform_* 方法
- mask 规则以 role-to-action 映射声明在配置中，与 chat_template 完全解耦
- 单次编码 + role-span 追踪替代两次编码 + 长度差计算 mask 的方式
- 支持多轮对话训练：所有 assistant 轮次参与训练，而非仅最后一轮
- 新建 astrai.preprocessing 包（builder.py + pipeline.py），删除 astrai/preprocess.py
- CLI 精简为 --config 参数，所有参数通过 PipelineConfig JSON 配置
- 新增 PipelineConfig、InputConfig、ProcessingConfig、OutputConfig dataclass
- 文档：assets/docs/preprocessing.md
- 27 个测试覆盖 mask builder、pipeline、配置序列化、工厂注册

astrai/preprocessing/pipeline.py

@@ -0,0 +1,134 @@
+"""Config-driven JSONL preprocessing pipeline.
+
+Composes a :class:`BaseMaskBuilder` (selected by ``input.type``) with
+deduplication, sharding, and flush to ``.h5`` / ``.bin`` storage.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import os
+from collections import defaultdict
+from typing import List, Optional
+
+import torch
+import tqdm
+
+from astrai.config.preprocess_config import PipelineConfig
+from astrai.dataset.storage import save_bin, save_h5
+from astrai.preprocessing.builder import MaskBuilderFactory
+from astrai.tokenize import AutoTokenizer
+
+
+def filter_by_length(text: str, min_len: int = 50, max_len: int = 2_000_000) -> bool:
+    return min_len <= len(text) <= max_len
+
+
+def dedup_signature(item: dict) -> str:
+    raw = json.dumps(item, sort_keys=True, ensure_ascii=False)
+    return hashlib.md5(raw[:200].encode()).hexdigest()
+
+
+class Pipeline:
+    """Tokenization pipeline driven by a declarative :class:`PipelineConfig`.
+
+    Usage::
+
+        config = PipelineConfig.from_json("sft_pipeline.json")
+        Pipeline(config, ["data.jsonl"], output_dir="out", tokenizer_path="params").run()
+    """
+
+    def __init__(
+        self,
+        config: PipelineConfig,
+        input_paths: List[str],
+        output_dir: str,
+        tokenizer_path: str,
+    ):
+        os.makedirs(output_dir, exist_ok=True)
+        self.config = config
+        self.paths = input_paths
+        self.output_dir = output_dir
+        self.tokenizer_path = tokenizer_path
+
+        self.mask_builder = MaskBuilderFactory.create(config.input.type)
+
+    def transform(self, item: dict) -> Optional[dict]:
+        return self.mask_builder.build(item, self.config, self._tokenizer)
+
+    def run(self):
+        self._tokenizer = AutoTokenizer.from_pretrained(self.tokenizer_path)
+
+        seen: set = set()
+        domains: dict = defaultdict(lambda: defaultdict(list))
+        total_tokens = 0
+        shard_idx: dict[str, int] = defaultdict(int)
+        count = 0
+
+        pp = self.config.preprocessing
+
+        for item in tqdm.tqdm(
+            self._iter_items(), desc="Tokenizing", unit="docs", mininterval=0.5
+        ):
+            if pp.max_items and count >= pp.max_items:
+                break
+
+            if pp.deduplicate:
+                sig = dedup_signature(item)
+                if sig in seen:
+                    continue
+                seen.add(sig)
+
+            result = self.transform(item)
+            if result is None:
+                continue
+
+            ids = result["ids"]
+            if not ids:
+                continue
+
+            domain = result.get("domain", "__default__")
+            domains[domain]["sequence"].append(ids)
+            if "loss_mask" in result:
+                domains[domain]["loss_mask"].append(result["loss_mask"])
+
+            count += 1
+            total_tokens += len(ids)
+
+            if total_tokens >= self.config.output.max_tokens_per_shard:
+                self._flush(domains, shard_idx)
+                domains.clear()
+                total_tokens = 0
+
+        if total_tokens > 0:
+            self._flush(domains, shard_idx)
+
+        print(f"Done. {count} documents tokenized.")
+
+    def _iter_items(self):
+        for path in self.paths:
+            with open(path, "r", encoding="utf-8") as f:
+                for line in f:
+                    line = line.strip()
+                    if not line:
+                        continue
+                    yield json.loads(line)
+
+    def _flush(self, domains, shard_idx):
+        for domain, keys in domains.items():
+            idx = shard_idx[domain]
+            tensors = {}
+            for key, ids_list in keys.items():
+                tensors[key] = [torch.tensor(sum(ids_list, []), dtype=torch.long)]
+            chunk_dir = os.path.join(self.output_dir, domain)
+            fmt = self.config.output.storage_format
+            if fmt == "bin":
+                save_bin(chunk_dir, tensors)
+            else:
+                save_h5(chunk_dir, f"data_{idx:04d}", tensors)
+            shard_idx[domain] = idx + 1
+            tqdm.tqdm.write(
+                f"  saved {domain}/shard_{idx:04d}  "
+                f"({tensors['sequence'][0].numel():,} tokens)"
+            )