ci: Add macOS CI builds (#17)

This change also introduces mise-en-place and `.tool-versions` to manage
Swift tool dependencies consistently on macOS and Linux.

.github/workflows/build.yaml

@@ -10,8 +10,11 @@ on:
   workflow_dispatch:
 
 jobs:
-  ubuntu-build:
-    runs-on: ubuntu-latest
+  build:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
     steps:
 
     - name: Checkout repository
@@ -21,6 +24,11 @@ jobs:
         fetch-depth: 0
         lfs: true
 
+    - name: Install the tool dependencies
+      uses: jdx/mise-action@v2
+      with:
+        experimental: true
+
     - name: Build, test, and release
       run: |
-        scripts/build-ubuntu.sh
+        scripts/build.sh

.tool-versions

@@ -0,0 +1 @@
+swift 6.0

scripts/build.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+
+set -e
+set -o pipefail
+set -x
+set -u
+
+# Remove the build directory if it exists to force a full rebuild.
+if [ -d .build ] ; then
+    rm -rf .build
+fi
+
+# Run the tests.
+swift test
+
+# Build the project.
+swift build