chore: [BREAKING] bump version to v4.0.0 (migration from Todoist REST API to Todoist API v1)

[pedroalves0]

🗺 Overview

This PR marks the release of the refactor that migrates the SDK from the Todoist REST API to the recently released Todoist API v1.

You can find a migration guide from v9 here, listing all the differences between API versions.

Relevant changes in this SDK

The SDK API remains largely unchanged, with the following exceptions:

• Some properties have been added to/remove from entities.

• Certain existing properties have been marked as required.

• The following methods are now paginated:

  - getTasks
  - getProjects
  - getProjectCollaborators
  - getSections
  - getLabels
  - getSharedLabels
  - getComments
  

• Two new methods added, moveTasks and getTasksByFilter.

This refactor ensures compatibility with the latest version of the Todoist Sync API while maintaining the familiar client API interface for consumers.

Note: This PR is mostly a formality. All important commits in this branch were already subject to review in their respective PRs.