manager_integ_tests: added Python integration test with lighthouse

[d4l3k]

This adds an E2E integration test that actually runs a training loop with the Manager and Lighthouse pieces.

This only tests the happy path currently and no recovery. Follow up PRs will add failure recovery tests.

To support instrumenting Python tests this adds bindings for Lighthouse.

Test plan:

tristanr@devvm5553 ~/torchft (d4l3k/integ_tests)> pytest torchft/manager_integ_test.py
==================================== test session starts ====================================
platform linux -- Python 3.10.14, pytest-8.3.3, pluggy-1.5.0
rootdir: /home/tristanr/torchft
configfile: pytest.ini
plugins: anyio-4.6.2.post1, typeguard-2.13.3
collected 1 item                                                                            

torchft/manager_integ_test.py .                                                       [100%]

===================================== 1 passed in 2.73s =====================================

The test is pretty fast ~2.73s but likely could be even faster with some tuning. We run 5 steps.