Improve Go test performance with t.Parallel()

Only **8.8%** of Go tests (62/706) use `t.Parallel()`.

**High-value targets:**
- `pkg/auth/service_test.go` - 36 tests
- `pkg/graveler/ref/manager_test.go` - 28 tests
- `esti/lakectl_test.go` - 28 tests
- `pkg/graveler/graveler_test.go` - 26 tests

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*Automation Initiative*