Only use config.x64_enabled as the memo cache key for canonicalize_dtype, not any other fields.
Only use config.x64_enabled as the memo cache key for canonicalize_dtype, not any other fields.

This saves the time to repeatedly build a tuple as a cache key. Reduces the time for CustomLinearSolveTest.test_custom_linear_solve_pytree on my workstation from 110s to 85s.

PiperOrigin-RevId: 422632700

google/jax,google/jax,google/jax,google/jax