Dockerfile tweaks

Dockerfile

@@ -4,7 +4,9 @@ RUN apk add --no-cache musl-dev openssl-dev pkgconfig openssl-libs-static
 FROM base AS builder
 WORKDIR /app
 COPY . .
-RUN cargo install --path .
+RUN --mount=type=cache,target=/app/target \
+    --mount=type=cache,from=base,source=/usr/local/rustup,target=/usr/local/rustup \
+    cargo install --locked --path .
 
 FROM alpine AS runtime
 COPY --from=builder /usr/local/cargo/bin/charms /usr/local/bin

src/lib.rs

@@ -1,5 +1,3 @@
-extern crate core;
-
 pub mod app;
 pub mod cli;
 pub mod script;