fix!: Big move to use kwargs as the initializer for classes which include us

[bougyman]

Hopefully this doesn't break anything yet, but after
discussing with @BryceARich I changed the way we assume
a class which includes us will define its initializer.

Before we were mandating a simple array of arguments,
this PR will mandate kwargs (Keyword Arguments) only
and raise and ArgumentError in #run if instance_args:
which are not a hash are passed to it.

[Copilot]

Pull Request Overview

This PR changes the way class initialization is handled in the NatsApiServer module, migrating from positional arguments to keyword arguments. The changes ensure that classes including the module must use keyword arguments in their initializers, providing better clarity and type safety.

• Adds validation to ensure instance_args is a Hash when provided
• Updates the worker instantiation to use keyword argument splat (**) instead of positional argument splat (*)
• Refactors parameter handling in build_worker method for consistency

Reviewed Changes

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

File	Description
lib/leopard/nats_api_server.rb	Adds Hash validation for instance_args and updates worker instantiation to use keyword arguments
lib/leopard/message_wrapper.rb	Adds header assignment in respond method
examples/echo_endpoint.rb	Updates example to use keyword arguments and includes debugging code