refactor: migrate to gitea actions

ci/setup-builder.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -eu
+docker compose -p openwrt-rust -f ci/cache.compose.yml up -d --wait
+if ! docker buildx inspect openwrt-sdk-rust >/dev/null 2>&1; then
+    docker buildx create --name openwrt-sdk-rust --driver docker-container \
+        --driver-opt network=host,memory=20g,memory-swap=20g,cpu-period=100000,cpu-quota=800000 \
+        --buildkitd-config ci/buildkitd.toml \
+        --buildkitd-flags '--allow-insecure-entitlement network.host' || \
+        docker buildx inspect openwrt-sdk-rust
+fi
+docker buildx inspect openwrt-sdk-rust --bootstrap