fix: ensure multiple integration test suites can run 🏃‍♀️

[ramiAbdou]

Description ✏️

This PR does the following:

• Converts the test suite to run in a single thread, instead of in parallel.
• Truncates all tables before each test.
• Process dotenv in the vitest config directly.
• Adds options to the migrate function, which now allows a Kysely instance to be passed in.
• Colocates database testing utilities and setup files in database/test.
• Adds global setup and per suite setup for integration tests.
• Updates documentation to setup .env.test file.

Type of Change 🐞

• Feature - A non-breaking change which adds functionality.
• Fix - A non-breaking change which fixes an issue.
• Refactor - A change that neither fixes a bug nor adds a feature.
• Documentation - A change only to in-code or markdown documentation.
• Tests - A change that adds missing unit/integration tests.
• Chore - A change that is likely none of the above.

Checklist ✅

• I have done a self-review of my code.
• I have manually tested my code (if applicable).
• I have added/updated any relevant documentation (if applicable).