[oryx] harvest does not sow constant jax values

It appears that sown values that are not input dependant does not appear in the harvested dictionary. I wonder if this is normal ?

import jax
from oryx.core.interpreters import harvest
import jax.numpy as jnp

jax.config.enable_omnistaging()


@jax.custom_vjp
def f(rng, x):
  rng, bwd_rng = jax.random.split(rng)
  # a = jax.random.uniform(rng)  # this work
  a = jnp.ones(2)
  harvest.sow(a, name="sown_fwd", tag="d")
  return x * a


def f_fwd(rng, x):
  return f(rng, x), (rng, )

def f_bwd(res, y):
  rng, = res
  # a = jax.random.uniform(rng)  # this work
  a = jnp.ones(2)
  harvest.sow(a, name="sown_bwd", tag="d")
  return None, a * y

def loss(x, rng):
  return f(rng, x).sum()


f.defvjp(f_fwd, f_bwd)


rng = jax.random.PRNGKey(33)
fwd_bwd = harvest.harvest(jax.value_and_grad(loss), tag='d')
(value, grad), harvest_output = jax.jit(fwd_bwd)({}, jnp.array([1., 1.]), rng)
print(harvest_output)
# Return {}

Start by running the Python reproducer using harvest.sow, harvest.harvest, jax.jit, and the custom VJP shown in the issue, comparing constant values with input-dependent values. Trace the harvest behavior for both forward and backward passes; done means determining whether constant sown values should appear in the harvested dictionary and documenting or correcting the behavior.