fix zig too

dockerfiles/zig-0.12.Dockerfile

@@ -1,4 +1,5 @@
-FROM alpine:3.19
+# syntax=docker/dockerfile:1.7-labs
+FROM alpine:3.20
 
 # Add the testing repository
 RUN echo "@community http://dl-cdn.alpinelinux.org/alpine/edge/community" >> /etc/apk/repositories
@@ -17,5 +18,15 @@ RUN echo "@community http://dl-cdn.alpinelinux.org/alpine/edge/community" >> /et
 # Update the package list and install Zig
 RUN apk add --no-cache zig@community=0.12.0-r0
 
+WORKDIR /app
+
+# .git & README.md are unique per-repository. We ignore them on first copy to prevent cache misses
+COPY --exclude=.git --exclude=README.md . /app
+
+RUN zig build
+
 RUN printf "set -e \ncd \${CODECRAFTERS_SUBMISSION_DIR} \necho 'Running zig build' \nzig build \necho 'zig build completed.' \n" > /codecrafters-precompile.sh
 RUN chmod +x /codecrafters-precompile.sh
+
+# Once the heavy steps are done, we can copy all files back
+COPY . /app