🧹 refactor: use testutil.TestdataPath in users module tests

[jackby03]

🎯 What: Removed local tdPath utility in internal/modules/users/module_test.go and refactored tests to use the shared testutil.TestdataPath from github.com/hardbox-io/hardbox/internal/modules/util/testutil.
💡 Why: Reduces duplicate path-resolving logic and improves consistency across the codebase testing utilities, in-line with the ongoing effort to consolidate test data path access methods (which already affected logging and auditd test modules).
✅ Verification: Verified by running go fmt ./internal/modules/users, resolving compilation errors from removed tdPath functions, and running the make test test suite and standard Go tests to ensure that the code behaves correctly without functionally altering test results.
✨ Result: A more maintainable and cleaner tests infrastructure for internal/modules/users.

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PR created automatically by Jules for task 7464997786048593753 started by @jackby03

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