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/method/static.wren

@@ -0,0 +1,13 @@
+class Foo {
+  bar { "on instance" }
+  static bar { "on metaclass" }
+
+  bar(arg) { "on instance " + arg }
+  static bar(arg) { "on metaclass " + arg }
+}
+
+io.write("on metaclass " + "arg") // expect: on metaclass arg
+io.write(Foo.new.bar)        // expect: on instance
+io.write(Foo.bar)            // expect: on metaclass
+io.write(Foo.new.bar("arg")) // expect: on instance arg
+io.write(Foo.bar("arg"))     // expect: on metaclass arg