fix(torrent): address minor review suggestions - safe int cast comment and named constant

Agent-Logs-Url: https://github.com/OpenListTeam/OpenList/sessions/2752452f-b9e2-4f09-a5f0-837ea189aa28

Co-authored-by: PIKACHUIM <[email protected]>

Author: Copilot

internal/offline_download/tool/transfer.go

@@ -18,6 +18,7 @@ import (
 	"github.com/OpenListTeam/OpenList/v4/internal/task"
 	"github.com/OpenListTeam/OpenList/v4/internal/task_group"
 	"github.com/OpenListTeam/OpenList/v4/pkg/http_range"
+	"github.com/OpenListTeam/OpenList/v4/pkg/torrent"
 	"github.com/OpenListTeam/OpenList/v4/pkg/utils"
 	"github.com/OpenListTeam/OpenList/v4/server/common"
 	"github.com/OpenListTeam/tache"
@@ -379,7 +380,7 @@ func tryRapidUpload189(t *TransferTask, file *os.File, fileSize int64) (model.Ob
 	}
 
 	// 计算整文件 MD5（旧接口只需要 fileMD5）
-	fileMD5, _, err := _189pc.ComputeSliceMD5sFromReader(file, 10*1024*1024)
+	fileMD5, _, err := _189pc.ComputeSliceMD5sFromReader(file, torrent.DefaultPieceSize)
 	if err != nil {
 		return nil, fmt.Errorf("计算 MD5 失败: %w", err)
 	}

pkg/torrent/bencode.go

@@ -209,6 +209,7 @@ func bencodeDecodeString(r *bytes.Reader) ([]byte, error) {
 	if length < 0 || length > 100*1024*1024 {
 		return nil, fmt.Errorf("bencode: string length out of bounds: %d", length)
 	}
+	// Safe to convert to int: bounds check above ensures length <= 100MB which fits in int32
 	data := make([]byte, int(length))
 	_, err = io.ReadFull(r, data)
 	if err != nil {