Fix thread-safety issues in concurrent code paths

[Copilot]

Fixes thread-safety issues in classes where async tasks write to shared state that is read by the main/render thread.

Changes

• ProfileViewerScreen: Volatile fields (hypixelProfile, playerProfile, entity, etc.) for visibility of async writes to render thread
• BackpackPreview: AtomicReferenceArray for storages to guarantee visibility and atomic operations across threads
• ItemRepository: Volatile itemsImported/filesImported flags for visibility across async loading and synchronous reads

Scope

Only code with verified concurrent access has been modified - specifically cases where:

• Async CompletableFuture tasks write to fields/collections
• Main or render thread reads those same fields/collections
• Without proper synchronization, visibility guarantees are not met

Code using CompletableFutures but without actual concurrent access to shared mutable state (e.g., sequential event handlers, serialized task queues) has not been modified.

Original prompt

Review and identify non-thread-safe code that could lead to race conditions or have unwanted effects. Review the use of concurrency, completable futures, and virtual threads.

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[kevinthegreat1]

Ok I didn't know it was going to make a pr...

[kevinthegreat1]

Don't make just random code thread-safe. Only check for thread safety in actual concurrent code that is being accessed by multiple threads.

[kevinthegreat1]

Don't make just random code thread-safe. Only check for thread safety in actual concurrent code that is being accessed by multiple threads.

[Copilot]

Don't make just random code thread-safe. Only check for thread safety in actual concurrent code that is being accessed by multiple threads.

Reverted changes to code without actual concurrent access. Kept only:

• ProfileViewerScreen: async writes, render thread reads
• BackpackPreview: async writes, render thread reads
• ItemRepository: async writes, main thread reads

Reverted DiscordRPCManager, SecretsTracker, and SkyblockerWebSocket (events/calls are sequential, no real concurrency).

Commit: 11a3eaa