test(v2/driver): add test coverage for cache, validation, and helper functions

Increase test coverage for the v2/driver package from 29.8% to 36.7% by
adding 58 new test cases targeting previously untested functions:

- util_test.go: inputParamConstant, inputParamComponent,
  inputParamTaskOutput, getItems
- cache_test.go: getFingerPrint, getFingerPrintsAndID, createCache
  (with mock cacheutils.Client)
- container_test.go: validateContainer
- dag_test.go: validateDAG
- root_dag_test.go: validateRootDAG
- driver_test.go: validateNonRoot, provisionOutputs
- resolve_test.go: InferIndexedTaskName

Signed-off-by: Jaison Paul <paul.jaison@gmail.com>

Author: jsonmp-k8