jax.random.chisquare: support method='approximate'
Part of #39314.
quantile bias test results:
```
$ python tools/evaluate_sampler_bias.py --sampler=chisquare --df=1.0 --method=approximate
================================================================================
Sampler Bias Evaluation: jax.random.chisquare
Arguments: {'df': 1.0, 'method': 'approximate'}
Num Samples: 1,000,000 | Seed: 0 | Dtype: float32
================================================================================
Quantile | Empirical | Analytical | Abs Error | Rel Error | Std Error | Z-Score
---------+-------------+-------------+-------------+-----------+------------+--------
0.001 | 1.54889e-06 | 1.5708e-06 | -2.1902e-08 | -1.3943% | 9.9296e-08 | -0.22
0.01 | 0.000157718 | 0.000157088 | +6.3001e-07 | +0.4011% | 3.1262e-06 | +0.20
0.05 | 0.00389642 | 0.00393214 | -3.5717e-05 | -0.9083% | 3.4325e-05 | -1.04
0.1 | 0.0157416 | 0.0157908 | -4.9137e-05 | -0.3112% | 9.5245e-05 | -0.52
0.25 | 0.10145 | 0.101531 | -8.0933e-05 | -0.0797% | 3.6386e-04 | -0.22
0.5 | 0.454677 | 0.454936 | -2.5904e-04 | -0.0569% | 1.0613e-03 | -0.24
0.75 | 1.32391 | 1.3233 | +6.0419e-04 | +0.0457% | 2.4198e-03 | +0.25
0.9 | 2.70763 | 2.70554 | +2.0895e-03 | +0.0772% | 4.7845e-03 | +0.44
0.95 | 3.84883 | 3.84146 | +7.3689e-03 | +0.1918% | 7.3088e-03 | +1.01
0.99 | 6.63903 | 6.6349 | +4.1351e-03 | +0.0623% | 1.7725e-02 | +0.23
0.999 | 10.819 | 10.8276 | -8.5327e-03 | -0.0788% | 5.8521e-02 | -0.15
Summary:
Max Absolute Error: 8.5327e-03
Max Relative Error: 1.3943%
Max Z-Score: 1.04
```
PiperOrigin-RevId: 952689869
