Minor refactor

[DJStompZone]

Refactor and update project dependencies

• Removed unused using directives across multiple files.
• Simplified object instantiation and using statements.
• Changed ImageIcon to a readonly struct for immutability.
• Simplified dictionary initialization with new C# syntax.
• Migrated from WebClient to HttpClient in Updater class.
• Updated project files to target newer frameworks and tools.
• Updated Newtonsoft.Json package to version 13.0.3.
• Marked submodules fNbt and utils.forms as dirty.
• Removed redundant and commented-out code.
• Used nameof for argument names in exception handling.
• Refactored switch statements to use pattern matching.
• Removed duplicate PackageReference from project file.