controller: fix vpc update

[zhangzujian]

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

What type of this PR

• Bug fixes

Which issue(s) this PR fixes:

1. fixes reference to nil pointer;
2. fixes modification of cached object;
3. remove logging without detailed information.

WHAT

🤖 Generated by Copilot at 1c16c27

Refactored some controller code to use deep copies and improve readability. Removed redundant log statements. Added more error details for ovn-sbctl command.

🤖 Generated by Copilot at 1c16c27

Sing, O Muse, of the mighty pull request
That the skilled developer wrought with care
To enhance the code of the subnet.go file
And fix the errors that lurked in there.

HOW

🤖 Generated by Copilot at 1c16c27

• Rename vpc to cachedVpc and create deep copies of the cached object before updating it in pkg/controller/subnet.go (link, link, link)
• Remove unused or redundant variables and log statements in pkg/controller/subnet.go and pkg/controller/vpc.go (link, link, link, link)
• Rename vpc to status and create a deep copy of the cached object's status before updating it in pkg/controller/vpc.go (link)
• Remove redundant log statements in pkg/ovs/ovn-nb-logical_router_route.go (link)
• Add command output to error log in pkg/pinger/ovn.go (link)