chore: reorganize test files into domain-specific subdirectories

- Moved unit tests for user authentication into `tests/unit/auth/`
- Relocated integration tests for payment processing to `tests/integration/payments/`
- Grouped API endpoint tests under `tests/api/` with separate files for each resource
- Updated test runner configuration to discover tests in new directory structure

test/variable/scope_while.wren

@@ -0,0 +1,7 @@
+// Body has its own scope.
+var a = "outer"
+var i = 0
+while ((i = i + 1) <= 1) var a = "inner"
+io.write(a) // expect: outer
+
+// TODO(bob): What about condition?