Fix CNS error handling in fsnotify to prevent possible IP address leaks

[Copilot]

Issue

In the releaseAll function of the CNS fsnotify package, when errors occur during file operations (opening or reading files), the code logs the error but continues execution. This can lead to the podInterfaceID variable having an empty string value, which when passed to releaseIP could potentially fail to release IP addresses properly.

Changes

This PR fixes the error handling in the releaseAll method to properly handle file operation errors:

1. Added continue statements after file open errors to skip to the next containerID in the loop
2. Moved the file.Close() call before checking for read errors to ensure the file is always closed regardless of read errors
3. Added a continue statement after file read errors to skip to the next containerID in the loop

Testing

Added a new test (TestReleaseAll) that verifies:

• The code handles invalid files correctly (e.g., directories that can't be opened for reading)
• Only valid files are processed and their IPs are released
• Invalid entries remain in the pendingDelete map for potential retry

Also updated existing tests to use temporary directories instead of trying to access root filesystem paths, ensuring more reliable test execution in different environments.

Fixes #3557.

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[MikeZappa87]

The filepath pkg might be a better option here, unsure if CNS runs on both windows/linux

[Copilot]

I've updated the code to use filepath.Join for path construction instead of string concatenation. This change improves cross-platform compatibility for both Windows and Linux environments. The update has been applied in all three instances where paths were being constructed (632dd28).

[MikeZappa87]

As a reader of the logs, do I have enough information here to troubleshoot? Keep in mind the reader might be not familiar with the code or be technical.

[Copilot]

I've enhanced the error log messages to provide much more context for troubleshooting. The updated logs now include the filepath, containerID, and clearer descriptions of the operations being performed. This makes the logs more helpful for users who might not be familiar with the code. These improvements have been implemented in commit ce76903.