Fix broken test suite, refresh docs, deps, and CI

[shehio]

What's in here

Fix: get_value_function_difference always raised, breaking value iteration and both policy iteration variants (3 tests were failing on develop). np.intersect1d wraps dict_keys of State objects in 0-d object arrays, so the intersection always came back empty — the original inverted == check masked this, and once that inversion was corrected in 789cfe6 the function raised on every call where the state sets differ (which is legitimate: value functions derived from a QFunction exclude terminal states). Now computes the intersection with set semantics and requires the smaller value function's states to be a subset of the larger one's — the assumption the downstream minimum-keys logic already made. Test suite goes from 43 passed / 3 failed to 46 passed.

Fix: UnboundLocalError in Monte Carlo control when stable_count <= 0 — new_policy was referenced after a loop that may never run; initialized to the starting policy, same pattern as the earlier fix in policy_iteration_sutton.

Docs: README now documents the project itself — which algorithms are implemented (value iteration, both policy iteration variants, MC prediction/control first- and every-visit) and where, package layout, runnable grid-world examples, and how to run the tests. Existing resource links kept.

Deps: requirements.txt slimmed from a 2019 full-venv freeze to the 3 real dependencies (numpy, pytest, mypy). The old file pinned poetry, keyring, tox-travis, an unrelated PyPI package named state, an unused matplotlib, and numpy==1.18.0, which no longer installs on current Python. This should also clear most of the open Dependabot alerts.

CI: dead Travis config replaced with GitHub Actions — travis-ci.org is gone and the config targeted Python 3.6/3.7; the workflow runs pytest on 3.11 and 3.12.

Hygiene: added missing __init__.py to src/monte_carlo and src/problems; .gitignore now covers .venv/, .pytest_cache/, *.egg-info/.

Verification

python -m pytest on Python 3.14 / numpy 2.5: 43 passed, 3 failed before; 46 passed after.

🤖 Generated with Claude Code