refactor: Improving query performance of iptablesEips using caching

[shane965]

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

What type of this PR

Examples of user facing changes:

• Features

Which issue(s) this PR fixes:

Fixes #(issue-number)

WHAT

🤖 Generated by Copilot at 5e4a6ba

Refactor controller package to improve performance, readability, and consistency. Use iptables eips lister and label selectors for QoS policy management. Simplify and fix iptables rule generation for vpc eip updates.

🤖 Generated by Copilot at 5e4a6ba

Sing, O Muse, of the mighty refactorings
That the skilled coders wrought on the controller
To enhance its performance and its beauty
With iptables and label selectors.

HOW

🤖 Generated by Copilot at 5e4a6ba

• Replace the fields package with the labels package and use the iptables eips lister instead of the kubeovn client for better performance and consistency in the controller package (link, link)
• Update the handleUpdateQoSPolicy function in qos_policy.go to use the iptables eips lister with label selectors and assign the eip variable directly from the eips slice (link, link)
• Update the calcDualSubnetStatusIP and calcSubnetStatusIP functions in subnet.go to use the iptables eips lister with label selectors (link, link)
• Update the handleUpdateVpcEip function in vpc_nat_gateway.go to use the iptables eips lister with label selectors and assign the eip variable directly from the eips slice (link, link)
• Update the addEipQoS and deleteEipQoS functions in vpc_nat_gw_eip.go to use the iptables eips lister with label selectors and check the QoS policy sharing status (link)

[github-actions]

• The commit message should be more descriptive and informative.
• In qos_policy.go, the import statement for fields is not used anymore, it should be removed.
• In qos_policy.go, the usage of c.config.KubeOvnClient.KubeovnV1().IptablesEIPs().List() can be replaced with c.iptablesEipsLister.List().
• In subnet.go and vpc_nat_gateway.go, the usage of c.config.KubeOvnClient.KubeovnV1().IptablesEIPs().List() can be replaced with c.iptablesEipsLister.List().
• In vpc_nat_gw_eip.go, the import statement for fields is not used anymore, it should be removed.
• In vpc_nat_gw_eip.go, the usage of c.config.KubeOvnClient.KubeovnV1().IptablesEIPs().List() can be replaced with c.iptablesEipsLister.List().
• In qos_policy.go, eips.Items can be replaced with eips.
• In subnet.go and vpc_nat_gateway.go, eips.Items can be replaced with eips.
• In vpc_nat_gw_eip.go, eips.Items can be replaced with eips.