Mitmproxy-rs

- Building from source does not require a protobuf compiler anymore.

- Improve transparent proxy functionality on macOS.

- Add transparent proxy functionality for macOS.
This will receive a proper announcement later on.
- Prefer a system-provided `PROTOC` env var if set.
- Split mitmproxy_rs into three Python packages: mitmproxy-rs, mitmproxy-windows, and mitmproxy-macos.
- `mitmproxy-rs` is a cross-platform package distributed both as sdist and wheels.
Building from source requires a Rust compiler only, and optionally a Protobuf compiler.
- `mitmproxy-windows` and `mitmproxy-macos` are distributed as precompiled wheels only on PyPI.
Both can be built from source using a full git checkout (see the [build-os-wheels] CI job).
Note that the macOS app needs to be signed and notarized using a valid Apple Developer Id for the system extension to work.

[build-os-wheels]: https://github.com/mitmproxy/mitmproxy_rs/blob/main/.github/workflows/ci.yml

- Fall back to system-provided `protoc` if `protoc-bin-vendored` is not available.

- Fix source distributions on Linux and macOS.

- `mitmproxy_wireguard` is now `mitmproxy_rs`.
As indicated by the name change, the scope of the project now goes beyond WireGuard.
- Add transparent proxy functionality for Windows.
This will receive a proper announcement later on.