## Summary
- Pin `feistel_cipher` to `1.0.0` in `mix.exs` and refresh `mix.lock` to
Hex package resolution.
- Update install/upgrade docs to match the `feistel_cipher v1.0.0`
migration guidance (`bits` -> `time_bits`/`data_bits`, upstream links).
- Modernize CI workflow defaults in `.github/workflows/elixir.yaml` for
current Elixir/OTP and cache action versions.

## Validation
- mix deps.get
- mix format --check-formatted
- mix compile --warnings-as-errors
- mix test
- mix docs
- mix hex.build