Fix a regression in prefix plugin which can cause data race

[liu-cong]

The code returns an internal podSet map which can be modified in a separate request goroutines. The fix is to return a deep copy of the map.

This regression was introduced in a recent refactor.

[netlify]

✅ Deploy Preview for gateway-api-inference-extension ready!

Name	Link
🔨 Latest commit	1496497
🔍 Latest deploy log	https://app.netlify.com/projects/gateway-api-inference-extension/deploys/6879ac043ae62c00088cdfe9
😎 Deploy Preview	https://deploy-preview-1188--gateway-api-inference-extension.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[kfswain]

/lgtm
/approve

Totally unrelated to the fix I do wonder if we should make the podSets value a bool instead of a struct. I kinda poked around and it didnt look like we are using the struct for anything. I've always seen sets represented with a bool value. But not a big deal, I just saw the struct and it made me curious

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kfswain, liu-cong

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [kfswain]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[nirrozenbaum]

/lgtm /approve

Totally unrelated to the fix I do wonder if we should make the podSets value a bool instead of a struct. I kinda poked around and it didnt look like we are using the struct for anything. I've always seen sets represented with a bool value. But not a big deal, I just saw the struct and it made me curious

why not using k8s set which encapsulates the map behind it? definitely more readable. see example:

gateway-api-inference-extension/pkg/epp/common/config/loader/configloader.go

Line 99 in 7182f8f

pluginNames := sets.New[string]() // set of plugin names, a name must be unique

gateway-api-inference-extension/pkg/epp/common/config/loader/configloader.go

Lines 106 to 109 in 7182f8f

	if pluginNames.Has(pluginConfig.Name) {
	return fmt.Errorf("plugin name '%s' used more than once", pluginConfig.Name)
	}
	pluginNames.Insert(pluginConfig.Name)