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>

scripts/test-docker.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# Test using Docker
+set -euo pipefail
+
+echo "=== Building Docker image ==="
+docker build -t btest .
+
+echo ""
+echo "=== Running btest server in Docker ==="
+docker run -d --name btest-test -p 2000:2000/tcp -p 2001-2100:2001-2100/udp -p 2257-2356:2257-2356/udp btest -s -v
+sleep 2
+
+cleanup() {
+    echo "Stopping Docker container..."
+    docker stop btest-test 2>/dev/null || true
+    docker rm btest-test 2>/dev/null || true
+}
+trap cleanup EXIT
+
+BTEST="./target/release/btest"
+cargo build --release
+
+run_timed() {
+    local desc="$1"; shift
+    echo ""
+    echo "--- $desc ---"
+    $BTEST "$@" &
+    local pid=$!
+    sleep 5
+    kill $pid 2>/dev/null || true
+    wait $pid 2>/dev/null || true
+}
+
+run_timed "TCP Download from Docker server" -c 127.0.0.1 -r
+run_timed "TCP Upload to Docker server" -c 127.0.0.1 -t
+run_timed "TCP Bidirectional" -c 127.0.0.1 -t -r
+
+echo ""
+echo "=== Docker server logs ==="
+docker logs btest-test
+
+echo ""
+echo "=== Docker tests completed ==="