Upstream `concatenate_stream_datum` from bluesky

[danielballan]

The function concatenate_stream_datum introduced in bluesky/bluesky#1897 may fit in well in this repository, for general use.

[evvaaaa]

Sounds good! I'd like to do a pre-release after this if that's acceptable.

Since the last release we've added a py.typed which allows for stricter type checking downstream on the documents, however we have the problem that this causes a linting error for RunStart(some_additional_property="blah") or EventDescriptor(some_additional_property="blah").

It'd be nice to hear from people whether adding a global ignore for this specific warning is worth the other benefits the py.typed brings us.