⚡ Bolt: Reuse expensive DateFormatter and ByteCountFormatter instances

[acebytes]

💡 What: Extracted ByteCountFormatter and ISO8601DateFormatter into a centralized, static Formatters enum.
🎯 Why: Instantiating DateFormatter, ISO8601DateFormatter, and relying on class methods for ByteCountFormatter in Foundation is computationally expensive. Reusing statically allocated instances avoids the overhead of repeated allocations in high-frequency formatting methods across views, view models, and CLI output logic.
📊 Impact: Reduces computational overhead and improves execution performance when formatting sizes and dates.
🔬 Measurement: Verify changes with codebase tests and standard code review; ensure all formatted strings (sizes and timestamps) display identically to their previous states.

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PR created automatically by Jules for task 17412456081582868883 started by @acebytes

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid shared non-Sendable formatter singletons

Formatters.byteCount (and similarly Formatters.iso8601) introduces mutable Foundation formatter instances as global static state in Sources/Cacheout/Models/Formatters.swift, which are non-Sendable and trigger strict-concurrency MutableGlobalVariable diagnostics (an error in Swift 6 mode). This also creates a real cross-actor access path because formatting now happens from both @MainActor code in CacheoutViewModel and cleaner-actor code in CacheCleaner.logCleanup, so the shared instance can be touched concurrently. The previous per-call/class-method usage avoided this shared mutable state; please confine formatter instances to a single actor/context or guard access with synchronization.

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