LazyArray.compute() should honor `out=` param

Right now this is not the case:

```python
a = blosc2.ones(10)
out = blosc2.zeros(1)
lexpr = blosc2.lazyexpr("sum(a)")
print(lexpr.compute(out=out))
print(f"out = {out[:]}")
```

output:

```
10.0
out = [0.]
```

when it should be something like:

```
<blosc2.ndarray.NDArray object at 0x119052a90>
out = [10.]
```