[harvest] Document or fix that sow/reap doesn't work with keyword arguments

Reproducing example:

```
from oryx.core.interpreters.harvest import sow, reap
import jax

@jax.jit
def f(x):
sow(x, tag="d", name="x")

@jax.jit
def g(x):
return reap(f, tag="d")(x=x)

g(5) # {}
```

Start with the sow and reap implementations in oryx/core/interpreters/harvest.py and reproduce the keyword-argument example from the issue. Determine whether the behavior should be fixed or documented, then verify that the chosen outcome explains or resolves g(x) returning {}.

Written by the indexing model from the issue text.