refactor: migrate to gitea actions

Dockerfile

@@ -1,13 +1,35 @@
 ARG SAFE_TARGET
 ARG VERSION
 
-FROM ghcr.io/openwrt/sdk:${SAFE_TARGET}-${VERSION}
+FROM ghcr.io/openwrt/sdk:${SAFE_TARGET}-${VERSION} AS tooling
 
+# The SDK runs on amd64 even when compiling for another OpenWrt target.
+USER root
+RUN curl -fsSL https://github.com/mozilla/sccache/releases/download/v0.18.0/sccache-v0.18.0-x86_64-unknown-linux-musl.tar.gz -o /tmp/sccache.tar.gz && \
+    echo '45f1447fbe231e3037bde351ef70677dd212216c8d62ae7ca409fecc4d6acc89  /tmp/sccache.tar.gz' | sha256sum -c - && \
+    tar -xzf /tmp/sccache.tar.gz -C /tmp && \
+    install -m 0755 /tmp/sccache-v0.18.0-x86_64-unknown-linux-musl/sccache /usr/local/bin/sccache && \
+    rm -rf /tmp/sccache.tar.gz /tmp/sccache-v0.18.0-x86_64-unknown-linux-musl
+USER buildbot
+
+FROM tooling AS configured
+ARG SAFE_TARGET
+ARG VERSION
+ENV SCCACHE_REDIS_KEY_PREFIX=openwrt-rust:${SAFE_TARGET}-${VERSION}: \
+    CARGO_INCREMENTAL=0
+COPY --chmod=0755 ci/build-rust.sh /usr/local/bin/build-rust
 RUN ./scripts/feeds update packages && \
     ./scripts/feeds install rust && \
+    printf '\nCONFIG_RUST_SCCACHE=y\n' >> .config && \
     make defconfig && \
-    sed -i 's/--set=llvm.download-ci-llvm=true/--set=llvm.download-ci-llvm=false/g' feeds/packages/lang/rust/Makefile; \
-    { make package/rust/host/compile -j$(nproc) || \
-      make package/rust/host/compile -j1 V=sc; } && \
-    rm -rf build_dir/host/rustc-*/rustc-*/build \
-           dl/rustc-*.tar.*
+    grep -qx 'CONFIG_RUST_SCCACHE=y' .config && \
+    sed -i 's/--set=llvm.download-ci-llvm=true/--set=llvm.download-ci-llvm=false/g' feeds/packages/lang/rust/Makefile && \
+    sed -i '/--set=llvm.download-ci-llvm=false/a\	--set=build.ccache=sccache \\' feeds/packages/lang/rust/Makefile && \
+    sed -i '/^define Host\/Compile/i RUST_BUILD_JOBS ?= 8' feeds/packages/lang/rust/Makefile && \
+    sed -i 's/--build-dir /--jobs=$(RUST_BUILD_JOBS) --build-dir /' feeds/packages/lang/rust/Makefile
+
+FROM configured AS sdk
+ARG JOBS=8
+# A non-secret endpoint on the runner; do not persist it in the published image.
+ARG SCCACHE_REDIS_ENDPOINT
+RUN build-rust