chore: import upstream snapshot with attribution

tools/setup_deepgemm_pythons.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Provision one bare Python per `requires-python` entry (or per argument) and
+# print their paths as ":"-separated DEEPGEMM_PYTHON_INTERPRETERS. Skip this
+# entirely if you already have interpreter paths.
+#
+# Usage:
+#   export DEEPGEMM_PYTHON_INTERPRETERS=$(tools/setup_deepgemm_pythons.sh)
+#   python setup.py bdist_wheel --dist-dir=dist --py-limited-api=cp38
+#
+# Optional: DEEPGEMM_VENV_PREFIX (default: /tmp/dgenv).
+set -euo pipefail
+
+if [ "$#" -eq 0 ]; then
+  # Derive the matrix from `requires-python = ">=3.X,<3.Y"` in pyproject.toml.
+  pyproject="$(dirname "$0")/../pyproject.toml"
+  spec=$(grep -E '^requires-python' "$pyproject" \
+         | grep -oE '>=3\.[0-9]+,<3\.[0-9]+')
+  lo=${spec#>=3.}; lo=${lo%%,*}
+  hi=${spec##*<3.}
+  set -- $(seq "$lo" $((hi - 1)) | sed 's/^/3./')
+fi
+
+prefix="${DEEPGEMM_VENV_PREFIX:-/tmp/dgenv}"
+mkdir -p "$prefix"
+
+paths=""
+for V in "$@"; do
+  venv="$prefix/$V"
+  # uv-managed Python ensures Python.h is present; system 3.X-dev packages
+  # on the manylinux / Ubuntu build bases are not always installed.
+  [ -x "$venv/bin/python" ] || \
+    uv venv --python "$V" "$venv" --python-preference only-managed --seed \
+      >/dev/null
+  paths="$paths:$venv/bin/python"
+done
+echo "${paths#:}"