Low-hanging optimizations for CI pipelines (#75)

This PR attempts to avoid bankrupting the company by running 15 minutes
of unit tests on unchanged code or re-downloading
`@fortawesome/fontawesome-pro` 5 times for every PR commit.

.github/workflows/pr-validation.yml

@@ -1,8 +1,6 @@
-name: Run formatter, linter and tests
+name: Run formatter and linter
 on:
-  merge_group:
   pull_request:
-  push:
     branches:
       - main
 
@@ -21,8 +19,8 @@ jobs:
       - name: Check Rust formatting
         run: cargo fmt --all -- --check
 
-  lint-and-test:
-    timeout-minutes: 30
+  lint:
+    timeout-minutes: 10
     strategy:
       max-parallel: 1
     runs-on: ubuntu-latest
@@ -40,6 +38,10 @@ jobs:
       - uses: dtolnay/rust-toolchain@1.76
         with:
           components: clippy
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 18
+          cache: npm
       - name: Install Linux dependencies
         run: |
               sudo apt-get update
@@ -55,5 +57,5 @@ jobs:
               git remote set-branches origin main
               git fetch --depth 1 origin main
               git branch main origin/main
-      - name: Run Nx-configured `lint` and `test` targets
-        run: npx nx affected -t lint test --base=main --head=HEAD
+      - name: Run Nx-configured `lint` targets
+        run: npx nx affected -t lint --base=main --head=HEAD

.github/workflows/prod-validation.yml

@@ -0,0 +1,46 @@
+name: Run unit tests
+on:
+  pull_request:
+    branches:
+      - production
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  test:
+    timeout-minutes: 30
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/bin
+            ~/.cargo/registry/index/
+            ~/.cargp/registry/cache/
+            ~/.cargo/git/db/
+            target/
+          key: ${{ runner.os }}-cargo-lint-and-test-${{ hashFiles('**/Cargo.toml') }}
+      - uses: dtolnay/rust-toolchain@1.76
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 18
+          cache: npm
+      - name: Install Linux dependencies
+        run: |
+              sudo apt-get update
+              sudo apt-get install -y --no-install-recommends \
+                libasound2-dev \
+                libudev-dev \
+                git
+      - name: Install JS dependencies
+        run: npm ci
+      - name: Ensure unambiguous `production`
+        if: github.ref != 'refs/heads/production'
+        run: |
+              git remote set-branches origin production
+              git fetch --depth 1 origin production
+              git branch production origin/production
+      - name: Run Nx-configured `test` targets
+        run: npx nx affected -t test --base=production --head=HEAD