Refactor test user and pack creation in analytics and market handlers

Commit notes

- Updated test user creation to use a consistent UUID for user IDs and email formatting across multiple test files, enhancing uniqueness and clarity. - Modified test pack creation to utilize a consistent UUID for pack IDs and slug generation, ensuring better identification and organization in tests. - Improved overall test structure by standardizing user and pack creation methods in `analytics_parallel_test.go`, `analytics_test.go`, `integration_test.go`, `library_test.go`, `market_test.go`, `pattern_test.go`, and related files.