Initial commit: MikroTik btest server & client in Rust

Full reimplementation of the MikroTik Bandwidth Test protocol:
- Server mode: accepts connections from MikroTik devices on port 2000
- Client mode: connects to MikroTik btest servers
- TCP and UDP protocols with bidirectional support
- MD5 challenge-response authentication
- Dynamic speed adjustment (1.5x algorithm)
- Status exchange matching original C pselect() behavior
- Docker support with multi-stage build

Tested against MikroTik RouterOS achieving:
- 1.05 Gbps server RX (single connection)
- 530 Mbps client TCP download
- 840 Mbps client TCP upload
- 433 Mbps client UDP download

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,28 @@
+# Stage 1: Build
+FROM rust:1.82-slim AS builder
+
+WORKDIR /build
+COPY Cargo.toml Cargo.lock ./
+COPY src/ src/
+
+RUN cargo build --release
+
+# Stage 2: Runtime (minimal image)
+FROM debian:bookworm-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY --from=builder /build/target/release/btest /usr/local/bin/btest
+
+# btest control port
+EXPOSE 2000/tcp
+# UDP data ports range
+EXPOSE 2001-2100/udp
+# UDP client ports range
+EXPOSE 2257-2356/udp
+
+ENTRYPOINT ["btest"]
+# Default: run as server
+CMD ["-s"]