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/arity.wren

@@ -0,0 +1,26 @@
+class Foo {
+  method { 0 }
+  method(a) { a }
+  method(a, b) { a + b }
+  method(a, b, c) { a + b + c }
+  method(a, b, c, d) { a + b + c + d }
+  method(a, b, c, d, e) { a + b + c + d + e }
+  method(a, b, c, d, e, f) { a + b + c + d + e + f }
+  method(a, b, c, d, e, f, g) { a + b + c + d + e + f + g }
+  method(a, b, c, d, e, f, g, h) { a + b + c + d + e + f + g + h }
+  method(a, b, c, d, e, f, g, h, i) { a + b + c + d + e + f + g + h + i }
+  method(a, b, c, d, e, f, g, h, i, j) { a + b + c + d + e + f + g + h + i + j }
+}
+
+var foo = Foo.new
+io.write(foo.method) // expect: 0
+io.write(foo.method(1)) // expect: 1
+io.write(foo.method(1, 2)) // expect: 3
+io.write(foo.method(1, 2, 3)) // expect: 6
+io.write(foo.method(1, 2, 3, 4)) // expect: 10
+io.write(foo.method(1, 2, 3, 4, 5)) // expect: 15
+io.write(foo.method(1, 2, 3, 4, 5, 6)) // expect: 21
+io.write(foo.method(1, 2, 3, 4, 5, 6, 7)) // expect: 28
+io.write(foo.method(1, 2, 3, 4, 5, 6, 7, 8)) // expect: 36
+io.write(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9)) // expect: 45
+io.write(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)) // expect: 55