v0.7.0

• Documents#initialize: Changed model_options default contract from Hash
  to #to_h in YARD docs and normalized with .to_h on assignment to ensure
  @model_options is always a Hash
• Documents#fetch_embeddings: Changed options keyword default from nil to
  {} to avoid passing nil to Ollama::Client#embed
• Splitters::Semantic#initialize: Changed model_options default from nil
  to {}, normalized with .to_h on assignment, and updated YARD type from
  [Hash, nil] to [#to_h]