automatically load_store() if store_path is specified

[dustymabe]

Going through an example like:

https://github.com/matrix-nio/matrix-nio/blob/eeace59baa634ab0ee747ba40a7a96a686a9e536/src/nio/client/async_client.py#L408-L416

It's not immediately clear to my why the example wasn't working. I was passing a store_path, but could never figure out why no files were getting created in the path and thus my token never got synced and loaded on the next run.

I had to look through the code to figure out I needed to call load_store() for it to actually do anything (either creating the store or loading from it).

Can we auto create the store with default values if the user specifies store_path?