[v1][Core] Clean up usages of SpecializedManager

[zhouwfang]

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Purpose

SpecializedManager was renamed as SingleTypeKVCacheManager, but there are some places where the term SpecializedManager hasn't been cleaned up.

Test Plan

N/A

Test Result

N/A

(Optional) Documentation Update

[github-actions]

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[gemini-code-assist]

Code Review

This pull request performs a simple but necessary cleanup, renaming an occurrence of the old SpecializedManager class name to SingleTypeKVCacheManager within a docstring. The change is correct and consistent with the PR's goal. The review did not identify any issues of high or critical severity.