Add compile_error! binary to powerpack crate

This directs people to install the `powerpack-cli` crate if they try to
install `powerpack` as a binary.

.github/workflows/build.yaml

@@ -34,7 +34,7 @@ jobs:
 
     - name: Clippy
       continue-on-error: ${{ matrix.toolchain == 'nightly' }}
-      run: cargo clippy --workspace --all-targets
+      run: cargo clippy --workspace --all-targets --all-features
 
     - name: Test
       run: cargo test --workspace

Cargo.toml

@@ -27,5 +27,8 @@ default = ["env"]
 detach = ["dep:powerpack-detach"]
 env = ["dep:powerpack-env"]
 
+# Private API: Prevents the compile_error! for the powerpack binary
+_internal_test = []
+
 [profile.release]
 strip = true

src/main.rs

@@ -0,0 +1,6 @@
+#[cfg(not(feature = "_internal_test"))]
+compile_error! {"you meant to install powerpack-cli: type `cargo install powerpack-cli`"}
+fn main() {
+    eprintln!("you meant to install powerpack-cli: type `cargo install powerpack-cli`");
+    std::process::exit(1);
+}