Fill out the foundation package.

src/python/_framework/foundation/_later_test.py

src/python/_framework/foundation/_timer_future.py

src/python/_framework/foundation/abandonment.py

src/python/_framework/foundation/callable_util.py

src/python/_framework/foundation/future.py

src/python/_framework/foundation/later.py

src/python/_framework/foundation/stream.py

src/python/_framework/foundation/stream_testing.py

src/python/_framework/foundation/stream_util.py