refactor: rename space _picodata_* -> _pico_* / _raft_*

src/storage.rs

src/traft/raft_storage.rs

test/conftest.py

test/int/test_basics.py

test/int/test_cas.py

test/int/test_compaction.py

test/int/test_couple.py

test/int/test_expelling.py

test/int/test_joining.py

test/int/test_migration.py

test/int/test_network_effects.py

test/int/test_replication.py

test/int/test_snapshot.py

test/int/test_sql.py