Enable JAX 64-bit mode for tests

Add jax.config.update("jax_enable_x64", True) at module level in conftest.py
so all tests run with float64 precision. This fixes the pre-existing failure
in test__curvature_matrix_via_psf_weighted_noise_two_methods_agree where
float32 rounding produced a max absolute error of ~0.008, exceeding the
1e-4 tolerance.

https://claude.ai/code/session_01B9sVEV54XWCa2LJw1C8gvv

Author: claude

test_autoarray/conftest.py

@@ -1,5 +1,8 @@
+import jax
 import jax.numpy as jnp
 
+jax.config.update("jax_enable_x64", True)
+
 
 def pytest_configure():
     _ = jnp.sum(jnp.array([0.0]))  # Force backend init