Convert project to .NET 8 console application for cross-platform support

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This PR converts the Azure Storage GZip Encoding tool from .NET Framework 4.5.2 to .NET 8, making it cross-platform and suitable for Linux environments including Jenkins pipelines.

Key Changes

Cross-Platform Support

The tool now runs natively on:

• Linux (x64) - Perfect for Jenkins pipelines and CI/CD systems
• Windows (x64)
• macOS (x64)

Self-contained executables are generated for all platforms, eliminating the need for .NET runtime installation.

Modernized Dependencies

• CommandLineParser: 1.9.71 → 2.9.1 (latest stable)
• Azure SDK: WindowsAzure.Storage 7.0.0 → Azure.Storage.Blobs 12.22.1 (modern Azure SDK v12)
• Logging: System.Diagnostics.Trace → Microsoft.Extensions.Logging (structured logging)
• Removed legacy dependencies now included in .NET runtime

Code Modernization

• Updated to async/await pattern for all Azure Storage operations
• Replaced legacy CloudStorageAccount with modern BlobServiceClient
• Improved error handling and structured logging
• Updated CommandLineParser syntax for v2.x compatibility
• Better memory management and resource disposal

Project Structure

• Migrated to modern SDK-style project file
• Removed .NET Framework artifacts (packages.config, App.config, AssemblyInfo.cs)
• Enabled nullable reference types for better code safety
• Added build targets for self-contained executables

Usage Examples

Linux/Jenkins Pipeline:

./asge -e .css .js -f assets -r -c "${AZURE_STORAGE_CONNECTION_STRING}"

Windows:

asge.exe -e .css -f myContainer -r -a myStorageAccount -k <key>

Jenkins Pipeline:

pipeline {
    agent any
    stages {
        stage('Compress Assets') {
            steps {
                sh './asge -e .css .js -f assets -r -c "${AZURE_STORAGE_CONNECTION_STRING}"'
            }
        }
    }
}

All original functionality is preserved while adding cross-platform compatibility and modern .NET features.

Fixes #2.

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