Bugfix: VPC api call failures could cause deletion of all nodes

[akaokunc]

Hello, I was trying find a bug in cooperation between linode LKE api provider and linode CCM to explain unexpected behavior which I have seen on few clusters. I'm not sure I found the root cause of the issue I was observing, but I do believe I have found at least related one.

Here's the possible failure chain:

1. GetVPCIPAddresses or GetVPCIPv6Addresses returns error, that error would only be logged but the node will be skipped on writing to cache, due to condition:

if len(options.Options.VPCNames) > 0 && len(vpcNodes[instance.ID]) == 0 {
    continue  // instance skipped — vpcNodes is empty due to the failed API call
}

2. InstanceExists returns false, nil for every node, because linodeByID finds nothing in the empty cache and returns cloudprovider.InstanceNotFound which InstanceExists converts to false, nil.

3. The cache is written with an empty map and lastUpdate is stamped nc.nodes = newNodes; nc.lastUpdate = time.Now(), so the bad data persists for the full TTL period (default 15s).

4. The K8s node lifecycle controller deletes such nodes.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.63%. Comparing base (fd29af4) to head (2fc95f7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #570      +/-   ##
==========================================
+ Coverage   73.31%   73.63%   +0.32%     
==========================================
  Files          19       19              
  Lines        2960     2958       -2     
==========================================
+ Hits         2170     2178       +8     
+ Misses        532      525       -7     
+ Partials      258      255       -3     

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