fix: replace os.ReadDir with fs.ReadDir(1) to avoid extra memory usage

[andyzhangx]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
fix: replace os.ReadDir with fs.ReadDir(1) to avoid extra memory usage

Which issue(s) this PR fixes:

Fixes #

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Special notes for your reviewer:

Release note:

none

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andyzhangx

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[Copilot]

Pull request overview

This PR optimizes memory usage in the ensureMountPoint function by replacing os.ReadDir(target) with f.ReadDir(1). The original implementation read all directory entries just to verify mount point accessibility, which could be expensive for directories with many files. The new implementation reads only a single entry, achieving the same validation purpose with significantly reduced memory footprint.

Changes:

• Added io import to handle io.EOF for empty directories
• Replaced os.ReadDir(target) with os.Open(target) followed by f.ReadDir(1)
• Added proper handling for empty directories (io.EOF case)

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[andyzhangx]

/retest