refactor(collections): move collection types from HandyControl.Controls to HandyControl.Collections (closes #241)

[omid-io]

Description

This PR resolves #241 by moving collection types (OptimizedObservableCollection, ThreadSafeObservableCollection, UndoRedoList, and UndoRedoObservableCollection) out of the HandyControl.Controls namespace into HandyControl.Collections.

Motivation

Previously, collection classes located in src/Shared/HandyControl_Shared/HandyControls/Tools/Collection/ were placed under namespace HandyControl.Controls;. Importing HandyControl.Controls in ViewModels polluted the VM scope and degraded MVVM separation. The codebase already utilizes HandyControl.Collections (e.g. ManualObservableCollection<T>), making it the natural home for these collection structures.

Changes

• Updated namespace from HandyControl.Controls to HandyControl.Collections in:
  • OptimizedObservableCollection.cs
  • ThreadSafeObservableCollection.cs
  • UndoRedoList.cs
  • UndoRedoObservableCollection.cs
• Updated DispatchedObservableCollection.cs import from using HandyControl.Controls; to using HandyControl.Collections;
• Preserved UTF-8 BOM encoding across all modified source files.

Closes #241.