Add inline depth feature

[daibva]

🎯 Add InlineAfterDepth Option for Depth-Based Inline Formatting

This PR introduces a new encoding option InlineAfterDepth that automatically switches to inline (flow) style formatting when YAML nesting depth exceeds a specified threshold. This feature is particularly useful for deeply nested configuration files, making them more compact while maintaining readability at higher levels.

✨ Features

• Automatic depth detection: Tracks current nesting depth during encoding
• Flexible configuration: Users can specify any depth threshold (0, 1, 2, etc.)
• Backward compatible: Feature is disabled by default, no impact on existing code
• Error handling: Validates negative depth values with proper error messages
• Comprehensive testing: Includes unit tests for various scenarios

📝 Usage Examples

Basic Usage

// Enable inline formatting after depth 1
data := map[string]interface{}{
    "database": map[string]interface{}{
        "host": "localhost",
        "port": 5432,
    },
}

// Using MarshalWithOptions
yaml, err := yaml.MarshalWithOptions(data, yaml.InlineAfterDepth(1))

// Using Encoder
var buf bytes.Buffer
enc := yaml.NewEncoder(&buf, yaml.InlineAfterDepth(1))
err := enc.Encode(data)

Real-world Example (Clash Configuration)

// Perfect for configuration files like Clash configs
yaml.MarshalWithOptions(clashConfig, yaml.InlineAfterDepth(1))

🔄 Before/After Comparison

Standard Format:

database:
  primary:
    host: localhost
    port: 5432
    credentials:
      username: admin
      password: secret

With InlineAfterDepth(1):

database:
  primary: {host: localhost, port: 5432, credentials: {username: admin, password: secret}}

With InlineAfterDepth(2):

database:
  primary:
    host: localhost
    port: 5432
    credentials: {username: admin, password: secret}

🔧 Implementation Details

• File Changes:

  • option.go: Added InlineAfterDepth() function with validation
  • encode.go: Enhanced Encoder struct with depth tracking fields and logic
  • inline_depth_test.go: Comprehensive test suite covering all scenarios

• Depth Tracking: Automatically increments/decrements depth when encoding complex types (structs, maps, arrays)

• Flow Style Switching: Temporarily enables flow style when depth exceeds threshold, restores original style afterward

🧪 Testing Coverage

• ✅ Basic functionality tests with different depth values
• ✅ Error handling for invalid inputs (negative depths)
• ✅ Complex nested structure scenarios
• ✅ Default behavior verification (feature disabled)
• ✅ Real-world usage examples with Clash configuration files
• ✅ All existing tests continue to pass

📊 Benefits

• File Size Reduction: Significantly reduces file size for deeply nested structures
• Improved Readability: Maintains readability at higher levels while compacting deep nesting
• Practical Application: Ideal for configuration files, API responses, and data serialization

📋 Files Modified

• option.go - New encoding option implementation
• encode.go - Depth tracking and inline formatting logic
• inline_depth_test.go - Comprehensive test suite
• .gitignore - Added examples/ directory to exclude temporary test files

🚀 Ready for Production

This feature has been thoroughly tested and is ready for production use. It provides a powerful new way to control YAML formatting based on structural complexity, making it especially valuable for configuration management and data serialization scenarios.