Hello, BaseX team and community!

Disclosure: I am not yet an expert on these issues and I have not fully studied the specs of XQuery.

Now that Async Module is incorporated, I am wondering about some basic properties of xquery.

Example:

```xquery

for $i in 1 to 10

return fetch:text("http://example.com/magic-story/for-number/" || $i)

```

It feels to me that the xquery processor is broken if it cannot figure out on its own that the fetch can be done in parallel.

Why does this not work out of the box? Can it work out of the box? Wouldn't it be able to do this in parallel if a flag `can-be-optimized-for-parallel-execution` was defined for the `fetch:text`?