Lataa Aria2 Next 2.4.6

## Summary

This release fixes a Linux startup compatibility regression in the standalone aria2-next engine. It
removes the runtime dependency on the OpenSSL legacy provider for ARC4 handling, so packaged builds
can start in environments where OpenSSL provider modules are unavailable or hidden by AppImage and
sandbox runtime paths.

## Changed

- ARC4 encryption now uses aria2-next's internal implementation consistently instead of selecting an
OpenSSL, libgcrypt, or nettle backend at build time.
- Unused ARC4 backend source files were removed from the maintained CMake source inventory.

## Fixed

- Fixed engine startup failure on Linux systems where OSSL_PROVIDER_load("legacy") could not find
the OpenSSL legacy provider module.
- Fixed AppImage and distribution runtime compatibility for environments that do not expose
/usr/lib/ossl-modules to the bundled engine.