feat: enable custom bitwise operators | and & in wren compiler and add test

Add INFIX_OPERATOR entries for TOKEN_PIPE and TOKEN_AMP with PREC_BITWISE precedence in the compiler's grammar rules, replacing the previous UNUSED entries. This allows user-defined classes to implement custom `|` and `&` operator methods.

Include a new test file `test/custom_operators/bitwise.wren` that defines Amp and Pipe classes with their respective operator methods to validate the feature works correctly.

test/custom_operators/bitwise.wren

@@ -0,0 +1,11 @@
+class Amp {
+  & that {
+    return
+  }
+}
+
+class Pipe {
+  | that {
+    return
+  }
+}