chore(ci): verify no_std build on aarch64-unknown-none

Previously, nothing in CI proved the crate actually works in `no_std`
environments — a desktop `cargo build` with `std` omitted from features
still resolves `std` through the target's sysroot. With this commit,
add a dedicated job that builds against `aarch64-unknown-none`, a
bare-metal target without any `std` crate, so any accidental `std`
reliance fails to link.

The job builds both the default configuration and `--features color`
to cover the feature matrix that is expected to work without `std`.

Author: Brandon Williams

.github/workflows/ci.yml

@@ -54,6 +54,17 @@ jobs:
       - uses: taiki-e/install-action@cargo-hack
       - run: cargo hack check --feature-powerset --no-dev-deps
 
+  no-std:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - run: rustup toolchain install stable --profile minimal
+      - run: rustup target add aarch64-unknown-none
+      # Build against a bare-metal target that has no `std` crate,
+      # so any accidental reliance on `std` fails to link.
+      - run: cargo build --target aarch64-unknown-none --no-default-features
+      - run: cargo build --target aarch64-unknown-none --no-default-features --features color
+
   semver:
     runs-on: ubuntu-latest
     steps: