move to testify for testing

[maxdml]

Use https://github.com/stretchr/testify in our tests. This reduces significantly the amounts of LoC in the tests.

[Copilot]

Pull Request Overview

This PR adopts the testify library for Go tests to reduce code verbosity and improve test readability. The change replaces manual error checking and assertion patterns with testify's assert and require functions.

• Adds testify/assert and testify/require dependencies to simplify test assertions
• Replaces verbose manual error checking patterns with concise testify functions
• Maintains the same test logic while significantly reducing lines of code

Reviewed Changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
go.mod	Adds testify dependency and moves goleak to direct dependencies
dbos/workflows_test.go	Replaces manual error checks and assertions with testify functions
dbos/utils_test.go	Simplifies error handling in test utility functions
dbos/serialization_test.go	Converts manual assertions to testify assertions
dbos/queues_test.go	Replaces verbose test patterns with testify equivalents
dbos/logger_test.go	Simplifies logger test assertions
dbos/dbos_test.go	Converts basic DBOS test assertions
dbos/client_test.go	Streamlines client test error handling and assertions
dbos/admin_server_test.go	Simplifies admin server test validations

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}