phase 0 + 1: repo bones and ETF codec

Repo scaffolding (LICENSE, Makefile, pyproject.toml, README) matching
unfeed conventions. Flat package layout, ruff config, Unlicense.

ETF codec covers the subset needed for gen_call against an Elixir node:
small/int/big_int, atom_utf8 (legacy atom_ext on decode), binary, nil,
list, small/large tuple, new_pid, newer_reference. Booleans round-trip
as atoms true/false; Python None as atom nil; str encodes to utf-8
binary to match Elixir convention.

Golden vectors were generated from real Erlang term_to_binary/1 output
(generator script at docs/etf_vectors.erl). Decode tests verify wire
compatibility; round-trip tests verify encoder consistency.

make all green: 58 passed, lint clean.

Next phases tracked in docs/ROADMAP.md (EPMD, handshake, channel,
gen_call, TLS, unfeed integration).

.gitignore

@@ -0,0 +1,12 @@
+.venv/
+__pycache__/
+*.pyc
+*.pyo
+.pytest_cache/
+.ruff_cache/
+.mypy_cache/
+build/
+dist/
+*.egg-info/
+.coverage
+htmlcov/