class_docstr: Class used to monitor and update the gradient/hessian information in Stochastic Gradient
  Trees.
  
  Represents the aggregated gradient/hessian data in a node (global node statistics), category,
  or numerical feature's discretized bin.
code: def update(self, gh: GradHess, w: float = 1.0):
      self.g_var.update(gh.gradient, w)
      self.h_var.update(gh.hessian, w)
      self.gh_cov.update(gh.gradient, gh.hessian, w)
  
imports: from __future__ import annotations
  import collections
  import copy
  import dataclasses
  import functools
  import math
  import sys
  import typing
  from river.base.typing import FeatureName
  from river.stats import Cov, Var
label_desc: Use image node_id 6 for calling the GradHessStats obj's underlying member method code with example usage: obj.update(gh, w) without return types