package:dart_mcp v0.3.1

• Fixes communication problem when a MCPServer is instantiated without
  instructions.
• Fix the content argument to PromptMessage to be a single Content object.
• Add new package:dart_mcp/stdio.dart library with a stdioChannel utility
  for creating a stream channel that separates messages by newlines.
• Added more examples.
• Deprecated the WithElicitationHandler interface - the method this required
  is now defined directly on the ElicitationSupport mixin which matches the
  pattern used by other mixins in this package.
• Change the schema parameter for elicitation requests to an ObjectSchema to
  match the spec.
• Deprecate the Elicitations server capability, this doesn't exist in the spec.