chore(lambda-layer): install rustup in AL2 image for libcst source build

libcst >=1.8 only ships aarch64 wheels for manylinux_2_28+. On Amazon
Linux 2 (glibc 2.26) pip falls back to building from source, which now
needs cargo (libcst is partly Rust). Install rustup with the minimal
profile so the source build can proceed.

AL2023 (used for py3.12+) ships glibc 2.34 and uses the prebuilt wheel,
so Dockerfile.al2023 is unaffected.

Author: kukushking

building/lambda/Dockerfile

@@ -41,6 +41,13 @@ RUN pip3 install --upgrade urllib3==1.26.16  # temporary to avoid https://github
 # In new CMake 4, compatibility with CMake < 3.5 has been removed.
 # Unpin CMake when arrow version shipped with lambda layers is updated.
 RUN pip3 install --upgrade cmake==3.31.6
+# libcst (a pyarrow 24+ build dep, used for build-time stub docstring extraction)
+# only ships manylinux_2_28 aarch64 wheels and falls back to a Rust build on AL2's
+# glibc 2.26. Install rustup so cargo is on PATH for that source build.
+RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | \
+    sh -s -- -y --profile minimal --default-toolchain stable
+ENV PATH="/root/.cargo/bin:${PATH}"
+
 # pyarrow 24+ build deps: scikit-build-core replaces setuptools; cython>=3.1 and
 # libcst (used for build-time stub docstring extraction) are required.
 RUN pip3 install --upgrade six "cython>=3.1" hypothesis uv build scikit-build-core "libcst>=1.8.6"