text: Title: SA kernel missing model attribute
  Body: Trying to load an MCMC run using an SA kernel into `arviz`, I ran into this issue: 
  
  ```
  def test_model(...)
      ...
  kernel = SA(test_model)
  mcmc_test = MCMC(kernel, ...)
  mcmc_test.run(...)
  
  data_test = az.from_numpyro(mcmc_test)
  ```
  
  which raises...
  ```---------------------------------------------------------------------------
  AttributeError                            Traceback (most recent call last)
  /tmp/ipykernel_20194/2118154136.py in <module>
  ----> 1 data_test = az.from_numpyro(mcmc_test)
  
  ~/miniconda3/envs/refit_fvs/lib/python3.9/site-packages/arviz/data/io_numpyro.py in from_numpyro(posterior, prior, posterior_predictive, predictions, constant_data, predictions_constant_data, coords, dims, pred_dims, num_chains)
      331         Number of chains used for sampling. Ignored if posterior is present.
      332     """
  --> 333     return NumPyroConverter(
      334         posterior=posterior,
      335         prior=prior,
  
  ~/miniconda3/envs/refit_fvs/lib/python3.9/site-packages/arviz/data/io_numpyro.py in __init__(self, posterior, prior, posterior_predictive, predictions, constant_data, predictions_constant_data, coords, dims, pred_dims, num_chains)
       91             self._samples = samples
       92             self.nchains, self.ndraws = posterior.num_chains, posterior.num_samples
  ---> 93             self.model = self.posterior.sampler.model
       94             # model arguments and keyword arguments
       95             self._args = self.posterior._args  # pylint: disable=protected-access
  
  AttributeError: 'SA' object has no attribute 'model'
  ```
  
  Looking at the source code and noticing that this works for NUTS and HMC, the missing piece in the SA class seems to be the `model` property... going to prepare a PR to add it in the same manner as it's found in NUTS and HMC classes. 