Extract seeker rollback helperRefactor

[hayabusa-cloud]

Summary

• Extract rollbackSeeker() helper to eliminate duplicated seeker rollback logic in Copy functions

Test plan

• Verify go test -race ./... passes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[Copilot]

Pull request overview

This PR refactors duplicated seeker rollback logic in the Copy functions by extracting a helper function and makes minor documentation improvements.

Changes:

• Extracted rollbackSeeker() helper function to eliminate three instances of duplicated seeker rollback logic
• Reformatted doc.go to follow standard Go package documentation conventions (comment before package declaration)
• Updated README section headings from "What this package is?" to "Overview" across all language versions

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
io.go	Added rollbackSeeker() helper function and replaced three duplicated seeker rollback code blocks with calls to the helper
doc.go	Moved package comment to precede package declaration and reformatted Note section for proper alignment
README.md	Changed section heading from "What this package is?" to "Overview"
README.zh-CN.md	Changed section heading from "这个包是做什么的？" to "概述" (Overview in Chinese)
README.ja.md	Changed section heading from "このパッケージは何ですか？" to "概要" (Overview in Japanese)
README.fr.md	Changed section heading from "À quoi sert ce package ?" to "Aperçu" (Overview in French)
README.es.md	Changed section heading from "¿Qué es este paquete?" to "Descripción general" (Overview in Spanish)