Update CommandHandler base class for System.CommandLine 2.0.0-beta5 compatibility

[Copilot]

Overview

This PR updates the CommandHandler<TOptions> base class to support System.CommandLine 2.0.0-beta5 API patterns while maintaining complete backward compatibility with existing command handlers.

Problem

System.CommandLine 2.0.0-beta5 introduces breaking changes that affect handler method signatures:

• Handler methods now use ParseResult instead of individual parameters
• SetHandler is replaced with SetAction
• New option creation patterns are required

The existing CommandHandler<TOptions> base class needed to be updated to support these new patterns without breaking existing functionality.

Solution

Key Changes

1. Enhanced ICommandHandler Interface

public interface ICommandHandler<TOptions> where TOptions : ICommandHandlerOptions
{
    // Existing method - unchanged
    Task HandleAsync(TOptions commandOptions);
    
    // New method for beta5 compatibility
    Task HandleAsync(ParseResult parseResult);
}

2. Updated CommandHandler Base Class

• Added virtual HandleAsync(ParseResult) method that delegates to the existing options-based method
• Added abstract ExtractCommandOptions(ParseResult) method for derived classes to implement
• Provided utility methods for ParseResult extraction:
  • GetOptionValue<T>(ParseResult, Option<T>)
  • GetOptionValue<T>(ParseResult, string)
  • HasOption(ParseResult, Option)

3. Migration Pattern
Command handlers implement the extraction method:

protected override MyCommandHandlerOptions ExtractCommandOptions(ParseResult parseResult)
{
    var projectPath = GetOptionValue<DirectoryInfo>(parseResult, "--project");
    var skipTables = GetOptionValue<bool>(parseResult, "--skipTables");
    return new MyCommandHandlerOptions(projectPath, skipTables);
}

Zero Breaking Changes

• ✅ All existing HandleAsync(TOptions) methods work unchanged
• ✅ All existing tests pass without modification
• ✅ All existing SetupCommand methods continue to work
• ✅ Legacy API remains fully functional until migration

Examples Updated

Updated three command handlers to demonstrate the new pattern:

• InitProjectCommandHandler
• ExtractModelCommandHandler
• QueryModelCommandHandler

Documentation

• Comprehensive migration guide (docs/COMMANDLINE-BETA5-MIGRATION.md)
• Practical before/after examples (docs/BETA5-MIGRATION-EXAMPLE.cs)
• Clear migration timeline and dependencies

Testing

Added test coverage for ParseResult functionality:

[TestMethod]
public async Task HandleAsync_WithParseResult_ShouldInitializeProjectDirectory_WhenProjectPathIsValid()
{
    // Demonstrates ParseResult-based handling works correctly
}

Benefits

1. Future Ready: Prepared for beta5 API when package is updated
2. Zero Downtime: Existing code continues working during migration
3. Type Safety: Strongly-typed options pattern preserved
4. Consistent: All command handlers follow the same extraction pattern
5. Testable: Both patterns can be easily unit tested

Next Steps

• Remaining command handlers can implement ExtractCommandOptions in follow-up PRs
• SetupCommand methods will migrate to SetAction after issues [Chore]: Update System.CommandLine package reference to 2.0.0-beta5 #15-16 are completed
• Package reference update to beta5 in issue [Chore]: Update System.CommandLine package reference to 2.0.0-beta5 #15

Fixes #17.

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