Fix assert equal chexify jit 387

[Sorata-kanda]

Fixes #387

Problem

chex.assert_equal fails with TracerBoolConversionError when used inside
@chex.chexify + @jax.jit decorated functions because it attempts to
compare traced values using unittest.TestCase().assertEqual().

Solution

Added a jittable implementation using jnp.array_equal() and converted
assert_equal from a static-only assertion to a value assertion, following
the same pattern as assert_trees_all_equal.

Changes

• Added _assert_equal_static() - original host implementation
• Added _assert_equal_jittable() - new jittable implementation using jnp.array_equal()
• Registered both with _value_assertion() so chexify can use the jittable version during tracing

Testing

All existing assert_equal tests pass. The original failing example now works:

@chex.chexify
@jax.jit
def f(x):
    chex.assert_equal(x, 0)
    return

f(0)  # Now works!