*: refactor methods to support mocking

Additionally, write some tests to ensure the driver method
`startBlacksmithBuilder` handles all exceptions correctly in
both nofallback=true and nofallback=false configurations.

.github/workflows/build.yml

@@ -0,0 +1,13 @@
+name: Build and Test
+on: [push, pull_request]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: '16'
+      - run: npm ci
+      - run: npm run build
+      - run: npm test