Improve release compression for smaller downloads

[Copilot]

Release packages were using default compression settings, resulting in unnecessarily large downloads.

Changes:

• ZIP packages: Added -9 flag for maximum compression (package-zip.sh, package-win.sh, package-macos.sh)
• Windows batch: Set CompressionLevel Optimal in PowerShell Compress-Archive (package-zip.bat)
• Linux package: Migrated from tar.gz to tar.xz for ~20-30% better compression (package-linux.sh)
• Documentation: Updated README.md and release.yml to reflect .tar.xz extension

Example:

# Before
tar -czf ${PACKAGE_NAME}.tar.gz ${PACKAGE_NAME}/

# After  
tar -cJf ${PACKAGE_NAME}.tar.xz ${PACKAGE_NAME}/

Bundled JRE packages will see the most benefit as they contain many uncompressed binaries.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Compress releases</issue_title>
<issue_description>Compress the releases more to make the file size smaller.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Compress releases #87

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