Refresh project dependencies

[gmile]

Summary

• refresh Hex dependencies, GitHub Actions, and benchmark code for current APIs
• standardize the development shell, package requirement, CI, and release workflow on Elixir 1.20.2 / Erlang/OTP 29.0.3
• expand CI to cover compilation warnings, formatting, unused dependencies, dependency cycles, unit tests, docs, Hex audit, the Nix flake, Dialyzer, and LibreOffice integration tests
• let pure unit tests run without LibreOffice while retaining explicit integration coverage
• update the LibreOffice test image path for the 26.2-only coverage
• remove the URP.Bridge / URP.Stream compile-time module cycle
• apply Elixir 1.20 compatibility fixes for pinned bitstring sizes and an unreachable private clause
• refresh Apple M3 Max performance figures against the updated runtime, dependencies, and live LibreOffice images
• repair the missing soffice-cli Compose service so every maintained benchmark script is reproducible

Validation

• nix flake check
• nix develop -c mix compile --warnings-as-errors
• nix develop -c mix format --check-formatted
• nix develop -c mix deps.unlock --check-unused
• nix develop -c mix xref graph --format cycles --fail-above 0
• nix develop -c mix test (40 passed, 40 integration tests excluded without local LibreOffice)
• nix develop -c mix docs --warnings-as-errors
• nix develop -c mix hex.audit
• nix develop -c mix dialyzer
• docker compose --file benchmarks/docker-compose.yml config --quiet
• nix develop -c mix run benchmarks/bench.exs
• nix develop -c env FIXTURE=benchmark-15mb.docx mix run benchmarks/bench.exs
• nix develop -c mix run benchmarks/io_bench.exs
• nix develop -c mix run benchmarks/convert.exs

The benchmark run used LibreOffice 26.2.4.2 for URP/Debian, 25.8.1.1 for URP/Alpine, and 26.2.2.2 for Gotenberg. The refreshed figures and stability caveats are recorded in PERFORMANCE.md.