feat: Add BingTextSearch ITextSearch<BingWebPage> LINQ implementation (PR3)

- Implements ITextSearch<BingWebPage> with LINQ filtering support
- Adds C# 14 MemoryExtensions.Contains compatibility
- Includes comprehensive unit tests for LINQ filter verification
- Adds NotSupportedException for collection.Contains patterns (Bing API limitation)
- Squashed from feature-text-search-linq-pr3 for clean dependency management

Author: alzarei