rename: Python module hebb → hebb_py

[ammar-s847]

Summary

The PyPI distribution is `hebb-py` (the bare `hebb` name is taken by an unrelated astronomy package, "Halo Extreme Bayesian Bootstrap"). Aligning the module name with the distribution name makes `pip install hebb-py` / `import hebb_py` self-consistent and avoids any chance of import collision with the astronomy package.

Changes

• `python/Cargo.toml`: `[lib] name = "hebb_py"` (was `"hebb"`). Controls the cdylib filename and therefore the Python module name.
• `python/src/lib.rs`: `#[pymodule] fn hebb_py(...)` (was `fn hebb(...)`).
• `python/src/cortex.rs`: `hebb.` Python-path references in doc-comments → `hebb_py.` (e.g., `hebb.seeds.random` → `hebb_py.seeds.random`). Rust paths (`hebb::*`) are unchanged.
• `README.md` / `CLAUDE.md` / `.github/workflows/ci.yml`: `import hebb` → `import hebb_py`, including the CI smoke test.
• `.gitignore`: also adds `/Cargo.lock` (accidentally tracked otherwise; libraries shouldn't ship a lock file).

Rust paths (`hebb::*`, `cargo add hebb`) and the crate name on crates.io are unchanged — this is a Python-side rename only.

Verification

• `cargo check --workspace --features disk` green
• `maturin build --release` produces `hebb_py-0.1.0-...whl`
• `pip install` + `import hebb_py; sim = hebb_py.Sim(); sim.run(1.0, 200)` → ran 13 spikes locally

Test plan

• CI green
• Manual: build wheel locally, install, `import hebb_py` works