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/comments/block.wren

@@ -0,0 +1,5 @@
+// In middle of line.
+io.write/* ... */(/* */"ok"/* */) // expect: ok
+
+// Nested.
+io.write(/* in /* nest */ out */"ok") // expect: ok

test/comments/block_at_eof.wren

@@ -0,0 +1,2 @@
+io.write("ok") // expect: ok
+/* comment */

test/comments/line_at_eof.wren

@@ -0,0 +1,2 @@
+io.write("ok") // expect: ok
+// comment