Add IAsyncEnumerable support for QueryAsync methods

[Copilot]

This PR implements IAsyncEnumerable<T> support for the QueryAsync methods in Azure Storage Table, enabling efficient streaming of large datasets without loading all results into memory at once.

New Features

🚀 New API Methods

• QueryAsyncEnumerable<T>(string partitionKey, int maxItems = 0)
• QueryAsyncEnumerable<T>(string partitionKey, IEnumerable<QueryFilter> queryFilters, int maxItems = 0)
• QueryAsyncEnumerable<T>(int maxItems = 0)
• Query<T>().AsAsyncEnumerable() for fluent API integration

💡 Usage Examples

// Stream large datasets efficiently
await foreach (var user in storageContext.QueryAsyncEnumerable<UserModel>("users", 1000))
{
    Console.WriteLine($"Processing user: {user.Name}");
    await ProcessUserAsync(user);
}

// With cancellation support
using var cts = new CancellationTokenSource(TimeSpan.FromMinutes(5));
await foreach (var product in storageContext
    .Query<Product>()
    .InPartition("electronics")
    .LimitTo(500)
    .AsAsyncEnumerable()
    .WithCancellation(cts.Token))
{
    // Process each product individually
}

// Memory-efficient processing of millions of records
await foreach (var order in storageContext.QueryAsyncEnumerable<Order>(maxItems: 1000000))
{
    totalValue += order.Amount;
    processedCount++;
    
    if (processedCount % 10000 == 0)
    {
        Console.WriteLine($"Processed {processedCount} orders...");
    }
}

Key Benefits

• Memory Efficient: Items are streamed one-by-one instead of loading entire result sets
• Performance: Lazy evaluation with early termination support
• Cancellation: Built-in CancellationToken support via WithCancellation()
• Developer Experience: Natural await foreach syntax
• Scalability: Process datasets of any size with constant memory usage

Framework Compatibility

IAsyncEnumerable support is available on:

• .NET Standard 2.1+
• .NET Core 3.0+
• .NET 5.0+
• .NET 8.0+

For older frameworks (.NET Standard 2.0, .NET Framework 4.8), the library automatically includes the Microsoft.Bcl.AsyncInterfaces package for compatibility.

Implementation Details

• Conditional Compilation: Uses #if NETSTANDARD2_1_OR_GREATER || NET5_0_OR_GREATER to enable features only where supported
• Azure Integration: Leverages existing Azure Table Storage pagination with AsPages().GetAsyncEnumerator()
• Backward Compatible: All existing QueryAsync methods continue to work unchanged
• Resource Management: Proper async disposal with IAsyncDisposable implementation

Technical Changes

• Added Microsoft.Bcl.AsyncInterfaces package dependency for older target frameworks
• Created StorageContextQueryIAsyncEnumerable<T> implementing IAsyncEnumerable<T>
• Created StorageContextQueryIAsyncEnumerator<T> implementing IAsyncEnumerator<T>
• Extended IStorageContext and query interfaces with async enumerable methods
• Integrated with existing query pipeline and filtering system

Testing

• ✅ Builds successfully on all target frameworks (netstandard2.0, netstandard2.1, net48, net8.0)
• ✅ Compilation and runtime functionality verified
• ✅ Backward compatibility maintained
• ✅ Integration with existing features (filters, pagination, delegates) confirmed

This enhancement provides a powerful new way to work with large datasets in Azure Table Storage while maintaining full backward compatibility with existing code.

Fixes #15.

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