added: profiling toolchain (py-spy, pyinstrument, pytest-benchmark, memray, snakeviz)

New `profile` optional-deps group, opt-in Pyinstrument ASGI middleware
gated by DECNET_PROFILE_REQUESTS, bench marker + tests/perf/ micro-benchmarks
for repository hot paths, and scripts/profile/ helpers for py-spy/cProfile/memray.

scripts/profile/memray-api.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+# Run the DECNET API under memray to capture an allocation profile.
+# Stop with Ctrl-C; then render with `memray flamegraph <bin>`.
+set -euo pipefail
+
+HOST="${DECNET_API_HOST:-127.0.0.1}"
+PORT="${DECNET_API_PORT:-8000}"
+OUT="${OUT:-profiles/memray-$(date +%s).bin}"
+mkdir -p "$(dirname "$OUT")"
+
+echo "Starting uvicorn under memray -> ${OUT}"
+python -m memray run -o "${OUT}" -m uvicorn decnet.web.api:app \
+    --host "${HOST}" --port "${PORT}" --log-level warning
+
+echo "Render with: memray flamegraph ${OUT}"