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/number/literals.wren

@@ -0,0 +1,10 @@
+io.write(123)     // expect: 123
+io.write(987654)  // expect: 987654
+io.write(0)       // expect: 0
+io.write(-0)      // expect: -0
+
+io.write(123.456) // expect: 123.456
+io.write(-0.001)  // expect: -0.001
+
+// TODO(bob): Hex? Scientific notation?
+// TODO(bob): Literals at and beyond numeric limits.