ipam: fix duplicate allocation after cidr expansion

[zhangzujian]

Pull Request

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What type of this PR

Examples of user facing changes:

• Features
• Bug fixes
• Docs
• Tests

Which issue(s) this PR fixes

Fixes #(issue-number)

WHAT

🤖[deprecated] Generated by Copilot at be11183

Fix IPAM bug and improve subnet CIDR handling. The pull request prevents address conflicts in dual-stack subnets and avoids re-assigning addresses when the subnet.Spec.CIDRBlock changes.

🤖[deprecated] Generated by Copilot at be11183

No more conflicts in the IPAM
We fixed the bug that caused them
We purged the code that was a sham
We reclaimed the power of our subnet

HOW

🤖[deprecated] Generated by Copilot at be11183

• Fix a bug in the calculation of the free and available IPv4 and IPv6 addresses in a subnet by considering the addresses that are already in use by existing pods (link, link)
• Remove a redundant and potentially harmful block of code that tried to re-add the already assigned addresses to the IPAM when the subnet CIDR changed, and rely on the sync logic in the SyncIPAM function instead (link, link)
• Ignore the no-op changes that resulted from a merge conflict or a formatting issue (link, link)