Add NO_EXTERNAL_TEST flag to skip tests using external APIs

Adds an externalTest(this) helper alongside slowTest that skips the test
when NO_EXTERNAL_TEST is set and raises the timeout to 60s, plus a
no-external-test script. Marks the tests hitting factorio.com, the mod
portal and GitHub with it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

package.json

@@ -10,6 +10,7 @@
 		"test": "pnpm run build && NODE_EXTRA_CA_CERTS=$(pwd)/test/file/tls/cert.pem mocha --enable-source-maps --check-leaks -R spec --recursive test \"plugins/*/test/**\" --exclude \"test/manual/**\"",
 		"silent-test": "SILENT_TEST=y pnpm test",
 		"fast-test": "FAST_TEST=y pnpm test",
+		"no-external-test": "NO_EXTERNAL_TEST=y pnpm test",
 		"cover": "nyc pnpm test",
 		"fast-cover": "FAST_TEST=y nyc pnpm test",
 		"ci-cover": "nyc --reporter=lcovonly pnpm run-script test",