[registry] Completion logs get mixed up during concurrent model generation

### Current Behavior

**Related issue in meshery:** https://github.com/meshery/meshery/issues/11036

When model generation runs for many models at once (via `InvokeGenerationFromSheetWithOptions`), the completion logs on stdout get mixed up.

Example of what users see:

Current model: jx-app-flagger
extracted 11 components for Jenkins Operator (jenkins-operator)
Current model: jx-app-kubeless
extracted 3 components for Jx App Flagger (jx-app-flagger)

The `Current model:` line and the `extracted N components for...` line don't always belong to the same model, which makes the output hard to follow.

This shows up when running `mesheryctl registry generate` because mesheryctl calls into meshkit — but the logging itself happens inside meshkit.

**Where in the code:** `registry/model.go`

- `InvokeGenerationFromSheetWithOptions` — completion logs after component generation (~lines 1013–1014)
- `GenerateDefsForCoreRegistrant` — same pattern for meshery registrant models (~lines 1161–1173)

Meshkit processes up to 20 models in parallel (`semaphore.NewWeighted(20)`). When each model finishes, it logs two separate lines (`Current model:` and `extracted ... components for ...`) from concurrent goroutines with nothing keeping those lines together.

### Expected Behavior

Each model's completion log should stay together and be readable — the model name in `Current model:` should match the model in the `extracted` line right below it.

### Environment

- **Host OS:** Linux (WSL2) — affects any OS running `mesheryctl registry generate`
- **Platform:** N/A (CLI / local generation; Docker or Kubernetes not required)
- **Meshery Server Version:** N/A
- **Meshery Client Version:** mesheryctl (uses meshkit v1.0.16+)