chore: import upstream snapshot with attribution

.github/actions/setup-pyenv/action.yml

@@ -0,0 +1,62 @@
+name: "setup-pyenv"
+description: "Setup pyenv"
+runs:
+  using: "composite"
+  steps:
+    ########## Ubuntu ##########
+    - name: Install python build tools
+      if: runner.os == 'Linux'
+      shell: bash
+      # Ref: https://github.com/pyenv/pyenv/wiki#suggested-build-environment
+      # Note: llvm is optional (required only for building PyPy/clang)
+      run: |
+        sudo apt-get update
+        sudo apt-get purge -y man-db || true
+        sudo apt-get install -y --no-install-recommends make build-essential libssl-dev zlib1g-dev \
+        libbz2-dev libreadline-dev libsqlite3-dev wget curl \
+        libncursesw5-dev xz-utils libffi-dev liblzma-dev
+    - name: Install pyenv
+      if: runner.os == 'Linux'
+      shell: bash
+      run: |
+        # Pin to pyenv v2.6.25 by tag + SHA verification for reproducible builds
+        git clone --branch v2.6.25 --depth 1 https://github.com/pyenv/pyenv.git "$HOME/.pyenv"
+        actual_sha=$(git -C "$HOME/.pyenv" rev-parse HEAD)
+        expected_sha="aa2e8b82605b8ba085dd15f7a31fe1990fabdcfa"
+        if [ "$actual_sha" != "$expected_sha" ]; then
+          echo "::error::pyenv SHA mismatch: expected $expected_sha, got $actual_sha"
+          exit 1
+        fi
+    - name: Setup environment variables
+      if: runner.os == 'Linux'
+      shell: bash
+      run: |
+        PYENV_ROOT="$HOME/.pyenv"
+        PYENV_BIN="$PYENV_ROOT/bin"
+        echo "$PYENV_BIN" >> $GITHUB_PATH
+        echo "PYENV_ROOT=$PYENV_ROOT" >> $GITHUB_ENV
+    - name: Check pyenv version
+      if: runner.os == 'Linux'
+      shell: bash
+      run: |
+        pyenv --version
+
+    ########## Windows ##########
+    - name: Install pyenv
+      if: runner.os == 'Windows'
+      shell: bash
+      run: |
+        uv pip install --system pyenv-win --target $HOME\\.pyenv
+    - name: Setup environment variables
+      if: runner.os == 'Windows'
+      shell: bash
+      run: |
+        echo "PYENV=$USERPROFILE\.pyenv\pyenv-win\\" >> $GITHUB_ENV
+        echo "PYENV_ROOT=$USERPROFILE\.pyenv\pyenv-win\\" >> $GITHUB_ENV
+        echo "PYENV_HOME=$USERPROFILE\.pyenv\pyenv-win\\" >> $GITHUB_ENV
+        echo "$USERPROFILE\.pyenv\pyenv-win\\bin\\" >> $GITHUB_PATH
+    - name: Check pyenv version
+      if: runner.os == 'Windows'
+      shell: bash
+      run: |
+        pyenv --version