convert: fix the qwen4exp lint and type-check failures

flake8 flagged an unused MmprojModel import, and ty flagged seven errors in
the PLE streaming path: eos_token_id can be absent, and _ple_map, _ple_path,
_ple_row_dim and _ple_rows_per_shard are all Optional at the declaration but
were dereferenced without narrowing.

The map is opened and the stride fixed before the first shard is written, and
_finish_ple_table only runs once every shard has landed, so the invariants
hold. Assert them so the checker can see it. A missing eos_token_id now raises
with the reason instead of a TypeError from int(None).

conversion/qwen4exp.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from pathlib import Path
 from typing import Iterable
 
 import torch
@@ -8,7 +9,7 @@ from torch import Tensor
 import gguf
 import numpy as np
 
-from .base import ModelBase, MmprojModel
+from .base import ModelBase
 from .qwen import _LinearAttentionVReorderBase, _Qwen35MRopeMixin
 from .qwen3vl import Qwen3VLVisionModel
 
@@ -36,8 +37,8 @@ class Qwen4ExpTextModel(_Qwen35MRopeMixin, _LinearAttentionVReorderBase):
         self._ple_shard_rows: dict[int, int] = {}
         self._ple_row_dim: int | None = None
         self._ple_rows_per_shard: int | None = None
-        self._ple_map = None
-        self._ple_path = None
+        self._ple_map: np.memmap | None = None
+        self._ple_path: Path | None = None
 
     def _read_hash_constants(self, suffix: str) -> list[int]:
         """Read an int64 PLE constant straight from the checkpoint.
@@ -106,6 +107,8 @@ class Qwen4ExpTextModel(_Qwen35MRopeMixin, _LinearAttentionVReorderBase):
         if isinstance(eos, list):
             # the PLE hash resets n-grams on the primary EOS
             return int(eos[-1])
+        if eos is None:
+            raise ValueError("eos_token_id is required: the PLE hash resets its n-grams on it")
         return int(eos)
 
     def modify_tensors(self, data_torch: Tensor, name: str, bid: int | None) -> Iterable[tuple[str, Tensor]]:
@@ -186,6 +189,8 @@ class Qwen4ExpTextModel(_Qwen35MRopeMixin, _LinearAttentionVReorderBase):
         return [(gguf_name + ".weight", table)]
 
     def _write_ple_shard(self, idx: int, shard: Tensor) -> None:
+        # the caller opens the map and fixes the stride before the first write
+        assert self._ple_map is not None and self._ple_rows_per_shard is not None
 
         rows = int(shard.shape[0])
         if idx != self.hparams["split_ngram_parts"] - 1 and rows != self._ple_rows_per_shard:
@@ -203,6 +208,9 @@ class Qwen4ExpTextModel(_Qwen35MRopeMixin, _LinearAttentionVReorderBase):
         del eager
 
     def _finish_ple_table(self, total_rows: int):
+        # only reached once every shard has been written, so the map is open
+        assert self._ple_map is not None and self._ple_path is not None
+        assert self._ple_row_dim is not None
 
         self._ple_map.flush()
         del self._ple_map