feat: Basic functionality for serving apis

[bougyman]

• feat: adds main lib and errors classes
• chore: Adds group to Gemfile
• feat: Adds basic message wrapper
• feat: Basic api server using message wrapper
• test: Adds test for message wrapper
• test: Adds tests for nats_api_server

This adds the NatsApiServer module, which provides a
basic API server with a message wrapper that runs
the message through middleware chain.

[Copilot]

Pull Request Overview

This PR introduces the NatsApiServer module for Rubyists::Leopard, providing a framework for building concurrent NATS Service API workers with middleware support and declarative endpoint definitions.

• Adds core infrastructure including settings, error classes, and message wrapper functionality
• Implements NatsApiServer module with endpoint registration, middleware chain, and concurrent worker management
• Provides comprehensive test coverage for all new components

Reviewed Changes

Copilot reviewed 18 out of 20 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
lib/leopard.rb	Main entry point with Pathname extension and SemanticLogger setup
lib/leopard/settings.rb	Configuration module using Dry::Configurable for libroot, root, and logger settings
lib/leopard/errors.rb	Base error classes for the framework
lib/leopard/message_wrapper.rb	JSON-aware wrapper for NATS messages with response helpers
lib/leopard/nats_api_server.rb	Core server module with endpoint registration, middleware support, and worker management
test/	Comprehensive test suite covering all new functionality
examples/echo_endpoint.rb	Simple usage example demonstrating endpoint definition
Gemfile	Groups development/test dependencies
Readme.adoc	Complete documentation with usage examples