Fix Velocity installation: handle selected_ram and ensure proper cancellation

[azozowsky]

Description

Fixed the Velocity installation process by properly handling the selected_ram variable and ensuring that cancellation works as expected.

Changes

• Set selected_ram in select_ram_8, select_ram_17, and select_ram_21.
• Set selected_ram in custom_ram_8, custom_ram_17, and custom_ram_21.
• Added skip_finalize check to ensure compatibility with other server types.
• Ensured no folder creation on cancellation in select_ram_* and custom_ram_*.
• Added debug logging in velocity_ram_selector.

Testing

• Verified that Velocity installation creates the folder, downloads the JAR, and generates the start script.
• Confirmed that cancellation in select_ram_* and custom_ram_* prevents folder creation.
• Ensured other server types (Paper, Spigot) are unaffected.