add unittest for IPAM

[zhangzujian]

• Make sure you have followed Kube-OVN Code Style.

What type of this PR

• Tests

Which issue(s) this PR fixes:

Fixes #(issue-number)

WHAT

🤖 Generated by Copilot at 785068c

This pull request enhances the ipam package by using the BigInt type for large IP ranges, fixing some bugs related to IP versions, and adding unit tests. It also updates the kubeovn API to use the BigInt type in the IPPoolStatus struct and implements the deep copy logic for it.

🤖 Generated by Copilot at 785068c

No more loss of precision in the IP range
We use the BigInt type to count every byte
We merge and split the subnets with rage
We test our code with fire and might

HOW

🤖 Generated by Copilot at 785068c

• Replace float64 with internal.BigInt to represent large numbers of IPs without losing precision (link, link, link, link, link, link, link, link, link, link, link)
• Fix bugs in NewIP, Add, and Sub methods of IP type that cause incorrect IP length or value (link, link, link)
• Fix bugs in Merge method of IPRangeList type that cause skipping adjacent ranges (link, link)
• Simplify NewIPRangeList function to accept variadic argument of IP type (link)
• Use NewEmptyIPRangeList function to create empty IPRangeLists instead of NewIPRangeList (link, link, link, link, link, link, link, link, link, link, link, link)
• Add unit tests for IP, IPRange, and IPRangeList types and methods in test/unittest/ipam package (link, link, link)