message: Add alloc to MethodsBuilder
  Summary:
  starlark_module proc-macro, when a function has default parameters, uses alloc to allocate the value to the heap.
  This was missing on MethodsBuilder
diff: @@ -437,6 +437,11 @@ impl MethodsBuilder {
  }),
  );
  }
  +
  + /// Allocate a value using the same underlying heap as the [`MethodsBuilder`]
  + pub fn alloc<'v, V: AllocFrozenValue>(&'v self, value: V) -> FrozenValue {
  + value.alloc_frozen_value(&self.heap)
  + }
  }
  /// Used to create methods for a [`StarlarkValue`](crate::values::StarlarkValue).
  