PackFileContainer improvement and load time improvements

[donkeyProgramming]

PR Classification

API and design refactor to improve abstraction, performance, and testability of pack file container management.

PR Summary

Introduces the IPackFileContainer interface, adds a cache-optimized read-only container for CA pack files, and implements a binary cache system to accelerate CA pack loading. Updates all code and tests to use the new abstractions and adds comprehensive unit tests.

• PackFileContainer.cs, CachedPackFileContainer.cs: Implement IPackFileContainer and add a read-only, cacheable container.
• PackFileService.cs: Refactored to operate on IPackFileContainer, supporting both mutable and read-only containers.
• PackFileContainerCacheHelper.cs: Implements binary cache serialization/deserialization for CA pack containers.
• PackFileContainerLoader.cs: Uses the cache for CA pack loading, with fallback and cache update logic.
• Extensive unit tests added for new abstractions and cache logic.