Update tutorial to use httpx2 #89

What is the problem or limitation you are having?

The BeeWare tutorial currently uses httpx in step 8, as we need to hit a HTTP API to retrieve JSON content using an async API.

Unfortunately, some recent events have led to questions around the maintenance of httpx; these events led to the emergence of a number of forks, including httpxyz and httpx2.

The maintainer of httpxyx blogged about the reasons for the fork; they followed up quickly with an endorsement of httpx2 as a "blessed" fork.

Describe the solution you'd like

The BeeWare tutorial should switch to using httpx2.

This is mostly a matter of replacing references to httpx with httpx2, as the two should be API compatible (although this should be verified).

There is one known discrepancy - on Android, truststore doesn't currently pick up the correct location for Android certificates (see sethmlarson/truststore#217). The current workaround is to add a verify=ssl.create_default_context() argument:

async with httpx2.AsyncClient(verify=ssl.create_default_context())

We don't need to modify the example code to accommodate this, as the tutorial doesn't suggest running on Android - but we should add a warning notifying people of the problem (referencing the upstream issue). The verify tag isn't needed on any other platform.

Describe alternatives you've considered

We could use a different fork, but httpx2 seems the best option at this point.

Additional context

No response