ci: nightly GitHub Action workflow

- Renames the nightly workflow test in '.github/workflows/nightly.yml'
- detects unused dependencies,
- detects Rust version becoming stale w.r.t. stable

Fixes #983

.github/workflows/nightly.yml

@@ -1,8 +1,11 @@
-name: Nightly tests on main
+# Nightly sanity checks
+name: nightly
 
 on:
+  workflow_dispatch: {}
+  # Once per day at 00:00 UTC
   schedule:
-    - cron:  '0 0 * * *'
+    - cron: "0 0 * * *"
 
 jobs:
   linux_exhaustive:
@@ -98,4 +101,9 @@ jobs:
           labels: |
             nightly
             automated issue
-  
+
+  unused-dependencies:
+    uses: lurk-lab/ci-workflows/.github/workflows/unused-deps.yml@main
+
+  rust-version-check:
+    uses: lurk-lab/ci-workflows/.github/workflows/rust-version-check.yml@main