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>

resources/extractor-jvm/THIRD_PARTY_NOTICES.txt

@@ -0,0 +1,12 @@
+Bundled JVM extractor dependencies:
+
+1) sevenzipjbinding (16.02-2.01)
+   - Maven artifact: net.sf.sevenzipjbinding:sevenzipjbinding
+   - Maven artifact: net.sf.sevenzipjbinding:sevenzipjbinding-all-platforms
+   - Upstream: https://sevenzipjbind.sourceforge.net/
+
+2) zip4j (2.11.5)
+   - Maven artifact: net.lingala.zip4j:zip4j
+   - Upstream: https://github.com/srikanth-lingala/zip4j
+
+Please review upstream licenses and notices before redistribution.