Derive debian13 library dir and Rust package from the architecture

- Make the libevent install patch take CMAKE_INSTALL_LIBDIR instead of
  hardcoding lib/x86_64-linux-gnu, and rename it to
  libevent-libdir-install.patch.
- Replace every hardcoded x86_64-linux-gnu in the debian13 Dockerfile with
  $(gcc -dumpmachine).
- Download the Rust tarball for `uname -m` and expose it to the Dockerfiles
  as the architecture-neutral rust-1.99.1.tar.xz (a hard link refreshed on
  every run), because podman cannot expand ARG in a --mount source.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

rocky9/Dockerfile

@@ -36,7 +36,7 @@ RUN dnf install --assumeyes --enablerepo=crb \
 
 RUN git config --global url."https://wangguofang.net/github.com/".insteadOf "https://github.com/"
 
-RUN --mount=type=bind,from=sources,source=rust-1.99.1-x86_64-unknown-linux-gnu.tar.xz,target=/tmp/rust.tar.xz \
+RUN --mount=type=bind,from=sources,source=rust-1.99.1.tar.xz,target=/tmp/rust.tar.xz \
     mkdir rust-src \
     && tar -xJf /tmp/rust.tar.xz -C rust-src --strip-components=1 \
     && rust-src/install.sh --prefix=/usr/local --without=rust-docs \