rename: picolib -> pico

src/main.rs

test/conftest.py

test/int/test_basics.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_shutdown.py

test/int/test_uninitialized.py

test/manual/test_benchmark.py