refactor: move benchmark directory under test and update all references

The benchmark directory is relocated from the project root into the test directory, and all scripts, documentation links, and gitignore paths are updated accordingly. The test runner is also refactored to explicitly walk subdirectories (core, io, language, limit) instead of using a single test root, and a new test/README.md is added to document the test suite structure. Additionally, the constructor test for the Foo class is updated to add a zero-arity constructor and adjust expected output strings.

test/language/this/closure.wren

@@ -0,0 +1,7 @@
+class Foo {
+  getClosure { new Fn { toString } }
+  toString { "Foo" }
+}
+
+var closure = (new Foo).getClosure
+IO.print(closure.call()) // expect: Foo

test/language/this/nested_class.wren

@@ -0,0 +1,22 @@
+class Outer {
+  method {
+    IO.print(this) // expect: Outer
+
+    new Fn {
+      IO.print(this) // expect: Outer
+
+      class Inner {
+        method {
+          IO.print(this) // expect: Inner
+        }
+        toString { "Inner" }
+      }
+
+      (new Inner).method
+    }.call()
+  }
+
+  toString { "Outer" }
+}
+
+(new Outer).method

test/language/this/nested_closure.wren

@@ -0,0 +1,7 @@
+class Foo {
+  getClosure { new Fn { new Fn { new Fn { toString } } } }
+  toString { "Foo" }
+}
+
+var closure = (new Foo).getClosure
+IO.print(closure.call().call().call()) // expect: Foo

test/language/this/this_at_top_level.wren

@@ -0,0 +1 @@
+this // expect error

test/language/this/this_in_method.wren

@@ -0,0 +1,6 @@
+class Foo {
+  bar { this }
+  baz { "baz" }
+}
+
+IO.print((new Foo).bar.baz) // expect: baz

test/language/this/this_in_static_method.wren

@@ -0,0 +1,10 @@
+class Foo {
+  static test {
+    IO.print(this == Foo) // expect: true
+    IO.print(this.bar) // expect: bar
+  }
+
+  static bar { "bar" }
+}
+
+Foo.test

test/language/this/this_in_top_level_function.wren

@@ -0,0 +1,3 @@
+new Fn {
+  this // expect error
+}