Move user listening logic to new client

[VoxSecundus]

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[Copilot]

Pull Request Overview

This PR refactors the user listening logic by extracting it from the UserClient into a new ListenClient class, creating better separation of concerns. The refactoring introduces a shared AuthenticatableClient base class to handle common authentication functionality.

• Extracted listen-related methods from UserClient to a new ListenClient class
• Created AuthenticatableClient base class for shared authentication logic
• Updated tests to reflect the new client structure and improved Response class handling

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
lib/overhear/clients/authenticatable_client.rb	New base class handling authentication logic shared between client classes
lib/overhear/clients/user_client.rb	Refactored to inherit from AuthenticatableClient, now only handles now_playing functionality
lib/overhear/clients/listen_client.rb	New client class containing listen-related methods (listen_count, listens)
test/test_listen_client.rb	New test file for ListenClient functionality
test/test_user_client.rb	Updated tests to focus on UserClient's remaining functionality
test/test_helper.rb	Added Response class for consistent test mocking
sig/overhear.rbs	Updated type signatures to reflect new class hierarchy
lib/overhear.rb	Added require statements for new client classes
lib/overhear/clients/client.rb	Fixed URL joining using URI.join

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