Add script to reproduce threading performance report results

Adds `reproduce_threading_report.sh` to run the WeaselDB server and
load tester configuration described in `threading_performance_report.md`.

Improvements over the original draft:
- Validates the build directory, config file, and required binaries
  before starting, and expects to be run from the project root.
- Wraps server shutdown and log printing in an EXIT/INT/TERM trap
  so the server is always cleaned up, even if the script is
  interrupted or the load tester fails.
- Makes the `ulimit -n` increase best-effort instead of fatal.
- Uses the existing `DURATION` variable consistently in the load
  tester invocation.
- Adds a final check that the unix socket was created before
  launching the load tester.
- Uses 2 connect threads on the client, which is sufficient for
  establishing 2000 connections over the 30-second run.

reproduce_threading_report.sh

@@ -0,0 +1,89 @@
+#!/bin/bash
+# Reproduce the threading performance report results.
+# Run from the project root, e.g.:
+#   ./reproduce_threading_report.sh
+set -euo pipefail
+
+BUILD_DIR="build"
+CONFIG="test_benchmark_config.toml"
+DURATION=30
+
+if [ ! -d "$BUILD_DIR" ]; then
+    echo "Error: build directory '$BUILD_DIR' not found. Build the project first." >&2
+    exit 1
+fi
+
+if [ ! -f "$CONFIG" ]; then
+    echo "Error: config '$CONFIG' not found. Run this script from the project root." >&2
+    exit 1
+fi
+
+if [ ! -x "$BUILD_DIR/weaseldb" ] || [ ! -x "$BUILD_DIR/load_tester" ]; then
+    echo "Error: required binaries not found in '$BUILD_DIR'. Build the project first." >&2
+    exit 1
+fi
+
+cd "$BUILD_DIR"
+
+# Increase file descriptor limit for high concurrency. Best-effort only:
+# it may fail if the hard limit is lower, especially in containers.
+ulimit -n 65536 2>/dev/null || echo "Warning: could not raise ulimit -n (continuing)" >&2
+
+# Clean up any leftover socket or server log from a previous run
+rm -f weaseldb.sock server.log
+
+SERVER_PID=""
+
+cleanup() {
+    if [ -n "$SERVER_PID" ] && kill -0 "$SERVER_PID" 2>/dev/null; then
+        echo ""
+        echo "=== Stopping server ==="
+        kill "$SERVER_PID" 2>/dev/null || true
+        wait "$SERVER_PID" 2>/dev/null || true
+    fi
+    echo "=== Server log tail ==="
+    tail -50 server.log 2>/dev/null || true
+}
+trap cleanup EXIT INT TERM
+
+echo "=== Starting WeaselDB server ==="
+./weaseldb --config "../$CONFIG" > server.log 2>&1 &
+SERVER_PID=$!
+
+echo "Server PID: $SERVER_PID"
+
+# Wait for server to be ready (unix socket created)
+for i in {1..30}; do
+    if [ -S weaseldb.sock ]; then
+        echo "Server ready after $((i * 100))ms"
+        break
+    fi
+    if ! kill -0 "$SERVER_PID" 2>/dev/null; then
+        echo "Server died unexpectedly"
+        cat server.log
+        exit 1
+    fi
+    sleep 0.1
+done
+
+if [ ! -S weaseldb.sock ]; then
+    echo "Error: server failed to create socket within 3 seconds" >&2
+    exit 1
+fi
+
+echo "=== Server log (first lines) ==="
+head -30 server.log
+
+echo ""
+echo "=== Running load tester ==="
+./load_tester \
+    --unix-socket weaseldb.sock \
+    --concurrency 2000 \
+    --requests-per-conn 500 \
+    --connect-threads 2 \
+    --network-threads 10 \
+    --duration "$DURATION" \
+    --stats-interval 1
+
+echo ""
+echo "=== Load test complete ==="