ci: add container build workflow

Add prebuilt build images and a publish workflow to speed CI by reusing heavy dependencies.

packages/containers/rust/Dockerfile

@@ -0,0 +1,13 @@
+ARG REGISTRY=ghcr.io/anomalyco
+FROM ${REGISTRY}/build/bun-node:24.04
+
+ARG RUST_TOOLCHAIN=stable
+
+ENV CARGO_HOME=/opt/cargo
+ENV RUSTUP_HOME=/opt/rustup
+ENV PATH=/opt/cargo/bin:/opt/bun/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+
+RUN set -euo pipefail; \
+  curl -fsSL https://sh.rustup.rs | sh -s -- -y --profile minimal --default-toolchain "${RUST_TOOLCHAIN}"; \
+  rustc --version; \
+  cargo --version