fix(handlers): nolint:unused waitAsyncForTest (golangci-lint v2 mc#1099)

waitAsyncForTest blocks until all goroutines launched via goAsync have
completed. It is intended for use in *_test.go files to prevent
goroutine leaks, but is defined in the production package to avoid
import cycles across test files in this package.

golangci-lint v2.x 'unused' linter catches it in production code.
Suppress with //nolint:unused since the function is intentionally
defined-but-not-called in production — it exists for tests.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace-server/internal/handlers/workspace.go

@@ -85,6 +85,11 @@ func (h *WorkspaceHandler) goAsync(fn func()) {
 	}()
 }
 
+// waitAsyncForTest blocks until all goroutines launched via goAsync have
+// completed. Intended for use in test files to prevent goroutine leaks;
+// defined here (not in the test package) so it can be used across all
+// *_test.go files in this package without import cycles.
+//nolint:unused
 func (h *WorkspaceHandler) waitAsyncForTest() {
 	h.asyncWG.Wait()
 }