is_jitted does not properly detect if inside a jit call (tested in version 0.4.12)

Since jax 0.4.12 (could be for other versions>0.4.1) the `is_jitted` function does not properly detect if inside a jit call.

```python
import jumpy

def f(a):
if jumpy.core.is_jitted():
print("JITTED")
else:
print("NOT JITTED")
return a*2

jax.jit(f)(1) --> NOT JITTED
```

Changing the `is_jitted` function to the following resolves the problem, but it is a very hacky fix. Also not sure about backward compatibility.

```python

def is_jitted() -> bool:
"""Returns true if currently inside a jax.jit call or jit is disabled."""
if jp.is_jax_installed is False:
return False
elif jax.config.jax_disable_jit:
return True
else:
return len(jax._src.core.thread_local_state.trace_state.trace_stack.stack) > 1
# return jax.core.cur_sublevel().level > 0

```