Fix ctl error handling

[lplewa]

CTL currently mixes POSIX int/errno returns with umf_result, and its “by_handle” handlers ignore errors from the underlying provider or pool, always returning success. All CTL functions should return umf_result (replace errno values with the corresponding enum) and each *_by_handle handler must propagate the exact umf_result it receives. This change will eliminate inconsistent error handling and prevent silent failures.