Code cleanup: remove dead code and fix bugs in GeneralUpdate.Core

[JusterZhu]

Summary

Systematic code review and cleanup of GeneralUpdate.Core — removing dead code, fixing bugs, and reducing duplication.

Changes

Bug Fixes

• WindowsStrategy.Execute(): Added missing override — previously inherited NotImplementedException from base class
• MacStrategy.Execute(): Fixed to delegate to ExecuteAsync() instead of skipping the entire update pipeline
• DownloadProgressReporter: Moved "all completed" event to orchestrator — previously fired on every single-asset completion instead of once after all downloads finish
• StorageManager.GetAllfiles: Returns empty list instead of null on exception, preventing NullReferenceException
• FileNode.GetHashCode(): Fixed to use Name + Hash instead of object identity, respecting Equals/GetHashCode contract
• ObjectTranslator.GetPacketHash(): Safe pattern-match cast replacing unsafe cast that could NRE
• MutiDownloadCompletedEventArgs: Fixed typo IsComplated to IsCompleted

Dead Code Removal

• Deleted FileTreeCore\FileTreeEnumerator.cs — 5 duplicate types in unused namespace
• Deleted IEventManager.cs — interface not implemented by EventManager, no references
• Removed unused _diffMode field from ClientUpdateStrategy
• Removed unused _script field and SetScript() from ConfiginfoBuilder
• Removed redundant DriverDirectory hiding base class property in GlobalConfigInfo
• Removed dead static field _compressionStrategy from CompressProvider
• Removed unused private constructor from VersionService
• Removed dead _hooks/_reporter fields from SilentPollOrchestrator
• Removed empty InfixOrder() methods from FileNode and FileTree

Code Deduplication

• Extracted StreamDownloadAsync() shared download loop, eliminating ~50 lines of duplicate code
• Added Hooks and Reporter properties to AbstractStrategy base class for subclass reuse
• Wired _customSkipOption in GeneralUpdateBootstrap to actual execution flow

Documentation

• Fixed corrupted UTF-8 character in UpdateOption.cs XML doc
• Removed stale script parameter from ProcessInfo.cs XML doc

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