style(test): change indentation from 4 spaces to 2 spaces

- Update all test files to use 2-space indentation
- Affects: test_buffer.cpp, test_shm.cpp, test_mutex.cpp
- Affects: test_semaphore.cpp, test_condition.cpp
- Affects: test_locks.cpp, test_ipc_channel.cpp
- Improves code consistency and readability

Author: mutouyun