fix(docker): improve build process with explicit file copying

Signed-off-by: JmPotato <github@ipotato.me>

Author: JmPotato

Dockerfile

@@ -15,23 +15,20 @@ WORKDIR /usr/src/app
 # Leverage a cache mount to /usr/local/cargo/registry/
 # for downloaded dependencies and a cache mount to /app/target/ for 
 # compiled dependencies which will speed up subsequent builds.
-# Leverage a bind mount to the src directory to avoid having to copy the
-# source code into the container. Once built, copy the executable to an
-# output directory before the cache mounted /app/target is unmounted.
-RUN --mount=type=bind,source=src,target=src \
-    --mount=type=bind,source=Cargo.toml,target=Cargo.toml \
-    --mount=type=cache,target=/app/target/ \
-    --mount=type=cache,target=/usr/local/cargo/registry/ \
-    <<EOF
-set -e
-cargo build --release
-EOF
+# Once built, copy the executable to an output directory before
+# the cache mounted /app/target is unmounted.
+COPY Cargo.toml ./
+COPY src ./src
+RUN --mount=type=cache,target=/usr/src/app/target \
+    --mount=type=cache,target=/usr/local/cargo/registry \
+    cargo build --release --bin ${APP_NAME} && cp ./target/release/${APP_NAME} ./${APP_NAME}
 
 ################################################################################
 # Create a new stage for running the application that contains the minimal
 # runtime dependencies for the application. This often uses a different base
 # image from the build stage where the necessary files are copied from the build
 # stage.
+
 FROM debian:bookworm-slim AS final
 ARG APP_NAME
 
@@ -51,7 +48,7 @@ RUN adduser \
 USER appuser
 
 # Copy the executable from the "build" stage.
-COPY --from=builder /usr/src/app/target/release/${APP_NAME} .
+COPY --from=builder /usr/src/app/${APP_NAME} .
 
 # Copy the necessary files.
 COPY templates ./templates