fix(worker-slice-config): return error on copier failure instead of continuing with zero-value gateway config

[mdryaan]

Description

In ReconcileWorkerSliceConfig, a copier.CopyWithOption failure at service/worker_slice_config_service.go:233 was logged and silently swallowed. Execution continued to line 275 where workerSliceConfig.Spec.ExternalGatewayConfig = externalGatewayConfig unconditionally wrote the zero-value struct to the Kubernetes API, erasing real gateway configuration on worker clusters. Replaced the log-and-continue with return ctrl.Result{}, err so the reconciler stops and controller-runtime requeues. Also removed the now-unused "go.uber.org/zap" import.

Fixes #399

How Has This Been Tested?

• service/worker_slice_config_service.go:233: the if err != nil branch previously called logger.With(zap.Error(err)).Errorf(...) and fell through; changed to return ctrl.Result{}, err. Verified the zero-value write at line 275 is now unreachable on copier failure.
• go build ./... passes with the change applied.
• make fmt passes with no diff.
• Pre-existing make vet and make unit-test failures (undefined: util.Client, unknown field ClusterName) are present on unmodified master and are unrelated to this change.

Checklist:

• The title of the PR states what changed and the related issues number (used for the release note).
• Does this PR requires documentation updates? — No.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas. — N/A.
• I have tested it for all user roles. — N/A, controller-level fix.
• I have added all the required unit test cases.

Does this PR introduce a breaking change for other components like worker-operator?

No

Fix ReconcileWorkerSliceConfig silently writing zero-value ExternalGatewayConfig to worker clusters when deep copy fails