[jax2tf] Improve the conversion of integer_pow for better numerical accuracy.
[jax2tf] Improve the conversion of integer_pow for better numerical accuracy.

Previously we simply converted integer_pow to tf.math.pow. JAX instead uses
a series of multiplications. We now use the same lowering strategy as JAX, so
that we have the same numerical result.

Also improved the error messages for assertion failures.

PiperOrigin-RevId: 373351147

google/neural-tangents