Implement safe recorder for improved concurrency in event streaming

[egasa21]

This pull request refactors the test code for the deploy event streaming handler to improve thread safety and reliability. The main change is the introduction of a custom safeRecorder to replace the standard httptest.NewRecorder() in tests that involve concurrent writes, ensuring thread-safe access to the response body.

Test infrastructure improvements:

• Introduced a thread-safe safeRecorder type to replace httptest.NewRecorder() in tests, preventing race conditions when accessing the response body during concurrent event streaming. (internal/server/handlers/deploy_test.go)
• Updated all affected tests to use newSafeRecorder() instead of httptest.NewRecorder(). (internal/server/handlers/deploy_test.go) [1] [2] [3]
• Replaced direct calls to rec.Body.String() with the new thread-safe method rec.BodyString(). (internal/server/handlers/deploy_test.go) [1] [2] [3]

Dependency updates:

• Added "bytes" import to support the new recorder implementation. (internal/server/handlers/deploy_test.go)…ming tests