Add vimeo/psalm and psalm/plugin-phpunit

[ghostwriter]

This pull request adds the Psalm as a development dependency to the project.

Psalm is a static analysis tool that can help identify errors in PHP code before it's even run, which can save time and improve the overall quality of the codebase.

Motivation

The motivation for adding Psalm as a dev dependency is to improve the quality of the project's codebase by catching potential errors before they can cause issues in production. By running Psalm as part of the development process, we can identify and fix these errors earlier in the development cycle, which can save time and effort in the long run.

Changes Made

• Added vimeo/psalm and psalm/plugin-phpunit to the composer.json file under the require-dev section.
• Added new psalm.xml.dist and psalm-baseline.xml files to the project, which includes the configuration settings for running Psalm.
• Added composer scripts

Scripts

composer check
composer test
composer phpunit
composer psalm

[ghostwriter]

Based on the changes in this pull request, it only adds Psalm, a development tool, and does not affect the userland code in any way. https://github.com/mockery/mockery/pull/1230/files

Therefore, I am going to proceed and merge this pull request to continue building on top of this.