feat: Adds graceful shutdown when INT/TERM/QUIT signal is received

[bougyman]

• refactor: Lowers AbcSize for building workers
• chore: move instance methods to an instance method module and update impacted tests
• feat: Adds Dry::Configurable extension, and makes #logger a configurable setting
• feat: Adds graceful termination of workers

[Copilot]

Pull Request Overview

This PR adds graceful shutdown functionality to the NATS API server, allowing it to properly handle INT/TERM/QUIT signals and cleanly terminate workers. It also refactors the codebase by moving instance methods to a dedicated module and introducing Dry::Configurable for better configuration management.

• Adds signal trapping for graceful shutdown of workers and thread pools
• Refactors code by separating instance methods into an InstanceMethods module
• Introduces Dry::Configurable extension and makes logger configurable

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 4 comments.

File	Description
lib/leopard/nats_api_server.rb	Implements graceful shutdown, adds instance methods module, and configurable logger
test/lib/nats_api_server.rb	Updates test require path and adapts tests for instance method refactoring