Test/comprehensive unit tests 13 (#397)

* test: add comprehensive unit tests for Sub Issue 13

Add comprehensive unit tests covering:
- Client/Upgrade mutual upgrade integration (ProcessInfo IPC, version chain, forcibly update)
- Differential upgrade full cycle (Clean/Dirty, binary files, nested directories, mixed operations)
- Event notification pipeline (all 7 event types, push upgrade simulation, multiple listeners)
- Parameter matrix combinations (UpdateOptions, Configinfo validation, auth schemes, blacklists)
- Real-world developer usage scenarios (minimal setup, full production chain, fluent API)
- StorageManager backup/restore tests
- PipelineContext and DiffPipeline tests

Results: CoreTest 111/112 pass, DifferentialTest 23/23 pass, ClientCoreTest 115/115 pass

* fix: rebase on master, fix namespaces, copilot suggestions and warnings

- Rebase on origin/master (merged project structure)
- Fix all namespace references to GeneralUpdate.Core.*
- Fix API changes: AppType enum, UpdateOptions, BlackListManager
- Fix copilot suggestions: encoding, tautology, mutations, unused vars
- Fix AddCustomOption empty list and Precheck callback tests

Results: CoreTest 165p, DifferentialTest 85p, ClientCoreTest 42p

* test: add Hooks integration, full parameter matrix, and configuration model tests

- BootstrapHooksAndExtensionsTests: Hook lifecycle (5 methods), RejectingHooks,
  UpdateContext/DownloadContext models, UpdateReport/UpdateEvent, IUpdateEventListener (8 methods), Security schemes
- BootstrapFullParameterMatrixTests: ALL 42 UpdateOptions constants with type coverage,
  6 combination chains (all 33 options, silent client, parallel diff, upgrade no backup, full security)
- ConfigurationModelsTests: BlackListConfig, HubConfig, DownloadAsset, DownloadPlan,
  DownloadProgress, DownloadResult, all 9 enum types, UpdateOption<T> value semantics

Results: CoreTest 283p/3f(pre-existing), all new tests pass

* test: add Client+Upgrade full dual-configuration integration tests

- Chain_ClientAndUpgrade_BothFullyConfigured: production deployment with
  Client and Upgrade bootstraps configured simultaneously with ALL
  non-conflicting parameters (30+ options each), hooks, listeners,
  extensions. Verifies independent instances.

- Chain_ClientAndUpgrade_CompleteDeveloperWorkflow: real-world developer
  flow showing complete API surface for both roles in a single method

* fix: add missing using System.Linq, fix encoding artifacts in test comments

* fix: use version-based sorting in CleanBackup instead of CreationTime to fix flaky test

Author: JusterZhu