feat: add io.write primitive and test runner with number literal tests

Implement the io.write() primitive function that prints a value followed by a newline, enabling basic output for testing. Add a Python test runner script (runtests) that discovers and executes .wren test files, comparing output against // expect: comments. Include initial number literal tests covering positive, negative, and zero values. Remove debug print statements from the VM interpreter and refactor primitive registration macros for cleaner code.

test/number_literals.wren

@@ -0,0 +1,6 @@
+io.write(123)    // expect: 123
+io.write(987654) // expect: 987654
+io.write(0)      // expect: 0
+io.write(-0)     // expect: 0
+
+// TODO(bob): Floating point numbers.