Convert LangchainRB to a Rails Engine

[lemingos]

Convert LangchainRB to a Rails Engine

Description

This PR transforms LangchainRB from a plain Ruby gem into a full-fledged Rails::Engine, enabling tighter Rails integration and better support for Rails applications.

Key Changes

1. Added Rails Engine Structure

• Created Langchain::Engine class inheriting from Rails::Engine
• Set up proper autoloading and eager loading paths
• Isolated the engine namespace to prevent conflicts
• add Response namespace to classes located in lib/langchain/llm/response directory

2. Rails Integration

• Added rails as a runtime dependency in gemspec
• Set up test/dummy Rails application for integration testing

3. Testing Infrastructure

• Added rspec-rails for Rails-specific testing
• Added Rails-specific test helpers and configurations

Benefits

• Namespace isolation all classas are now scoped to Langchain
• Better Rails Integration: Seamless integration with Rails applications
• Easier Configuration: Standard Rails initializers and configurations
• Improved Testing: Better test coverage with Rails integration tests
• Future Extensibility: Foundation for adding persistance layer

Breaking Changes

• This change makes Rails a required dependency

Testing

• All existing tests pass

[Copilot]

Pull Request Overview

Convert the LangchainRB gem into a Rails Engine for tighter Rails integration and namespaced response classes.

• Introduced a Rails::Engine and ApplicationRecord for engine structure and autoloading.
• Refactored all LLM adapter response classes under Langchain::LLM::Response namespace.
• Updated gemspec, Gemfile, Rakefile, and test/setup files for Rails dependency and dummy app testing.

[mvz]

This makes langchainrb depend on Rails. Is that intentional and what will the relation be with langchainrb_rails? I'm currently using langchainrb in contexts that do not involve Rails at all.

[ebababi]

For what it's worth, we were also using langchainrb in contexts that don't involve Rails at all. As already mentioned, shouldn't this tighter Rails integration be part of langchainrb_rails?