class_docstr: Designed for use as a fixture in tests.
  
  !!! Example
  
      ```python
      # tests/conftest.py
  
      @pytest.fixture
      def getkey():
          return eqxi.GetKey()
      ```
  
  Do not use this in any other context; the random seed generation gives deliberate
  non-determinism.
code: def __call__(self):
      self.call += 1
      return jr.fold_in(self.key, self.call)
  
file_path: equinox/equinox/internal/_getkey.py
imports: import dataclasses
  import random
  from typing import Optional
  import jax.random
  from jaxtyping import PRNGKeyArray
  from .._config import EQX_GETKEY_SEED
label_desc: Use image node_id 2 for calling the GetKey obj's underlying member method code with example usage: obj.__call__() and returns: jr