fix(doubao_new): remove temp file after cross-storage put

[Suyunmeng]

Summary / 摘要

• Fixed a bug where cross-storage copy uploads to Doubao New could leave temp/file-* temporary files after upload completion.

• In drivers/doubao_new/driver.go, the upload temp file created via utils.CreateTempFile is now always cleaned by defer with Close + Remove.

• User-visible behavior change: after copy tasks complete, temporary files generated for this upload path are cleaned up, preventing Temp directory growth and disk exhaustion.

• Important implementation note: no upload protocol logic was changed; this is a lifecycle cleanup fix only.

• Scope note: this PR does not introduce a global upload framework change; existing drivers that use os.CreateTemp were checked and already perform Close + Remove in defer.

• This PR has breaking changes.
  / 此 PR 包含破坏性变更。

• This PR changes public API, config, storage format, or migration behavior.
  / 此 PR 修改了公开 API、配置、存储格式或迁移行为。

• This PR requires corresponding changes in related repositories.
  / 此 PR 需要关联仓库同步修改。

Related repository PRs / 关联仓库 PR:

• OpenList-Frontend:
• OpenList-Docs:

Related Issues / 关联 Issue

Fixes #2529

Testing / 测试

• go test ./...
• Targeted test: go test ./drivers/doubao_new
• Manual test / 手动测试:
  Not executed in this change set.

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• I have formatted the changed code with gofmt, go fmt, or prettier where applicable.
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