ChainContext class

Shared execution context for chain steps that provides metadata storage and execution control capabilities.

Key features:

• Type-safe metadata storage
• Execution timeout control
• Chain abortion mechanism
• Cross-step communication

Example:

final context = ChainContext(
  timeout: Duration(seconds: 30),
  initialMetadata: {'feature_enabled': true},
);

// Store and retrieve metadata
context.addMetadata('key', 'value');
final value = context.getMetadata<String>('key');

// Control execution
context.shouldAbort = true;