Replace extraction backend with SevenZipJBinding + Zip4j JVM sidecar

- New JVM sidecar (resources/extractor-jvm/) using SevenZipJBinding for
  RAR/7z/TAR and Zip4j for ZIP multipart, matching JDownloader 2 stack
- Auto/JVM/Legacy backend modes via RD_EXTRACT_BACKEND env variable
- Fallback to legacy UnRAR/7z when JVM runtime unavailable
- Fix isJvmRuntimeMissingError false positives on valid extraction errors
- Cache JVM layout resolution to avoid repeated filesystem checks
- Route nested ZIP extraction through JVM backend consistently

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/extractor.test.ts

@@ -2,15 +2,25 @@ import fs from "node:fs";
 import os from "node:os";
 import path from "node:path";
 import AdmZip from "adm-zip";
-import { afterEach, describe, expect, it } from "vitest";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import { buildExternalExtractArgs, collectArchiveCleanupTargets, extractPackageArchives } from "../src/main/extractor";
 
 const tempDirs: string[] = [];
+const originalExtractBackend = process.env.RD_EXTRACT_BACKEND;
+
+beforeEach(() => {
+  process.env.RD_EXTRACT_BACKEND = "legacy";
+});
 
 afterEach(() => {
   for (const dir of tempDirs.splice(0)) {
     fs.rmSync(dir, { recursive: true, force: true });
   }
+  if (originalExtractBackend === undefined) {
+    delete process.env.RD_EXTRACT_BACKEND;
+  } else {
+    process.env.RD_EXTRACT_BACKEND = originalExtractBackend;
+  }
 });
 
 describe("extractor", () => {