feat: add multi-engine regex flavour support

scripts/build-engines.mjs

@@ -37,20 +37,34 @@ const packageJson = JSON.parse(
 );
 const engineDirectory = path.join(root, "public", "engines");
 const entries = (await readdir(engineDirectory)).sort();
+const expectedEntries = [
+  "README.md",
+  "cpp",
+  "dotnet",
+  "go",
+  "java",
+  "pcre2",
+  "perl",
+  "php",
+  "python",
+  "ruby",
+  "rust",
+];
 
 if (
   typeof packageJson.version !== "string" ||
-  entries.length !== 4 ||
-  entries[0] !== "README.md" ||
-  entries[1] !== "java" ||
-  entries[2] !== "pcre2" ||
-  entries[3] !== "python"
+  entries.length !== expectedEntries.length ||
+  entries.some((entry, index) => entry !== expectedEntries[index])
 ) {
   throw new Error(
-    "The production build requires the documented Java, PCRE2 and Python runtime packs.",
+    "The production build requires every documented checked-in runtime pack.",
   );
 }
 
 console.log(
-  "The checked-in Java, PCRE2 and Python runtime packs are present; no release-time download or engine compilation is needed.",
+  `The checked-in ${expectedEntries
+    .filter((entry) => entry !== "README.md")
+    .join(
+      ", ",
+    )} runtime packs are present; no release-time download or engine compilation is needed.`,
 );