Make all read methods available on DataFusion module

[ion-elgreco]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Instead of having users explicitly create a sessioncontext, we could just create one when not passed.

Describe the solution you'd like
Expose read methods in datafusion so you do this:

import datafusion as fun   # :D 

df = fun.read_parquet("my.parquet)"

I am curious on other peoples thoughts on this.

[timsaucer]

I think this works well for testing of a single DF, but wouldn't this lead to creating multiple session contexts for every file you access?

[Michael-J-Ward]

We could introduce a fn default_context() that also uses OnceLock similar to what we do for the TokioRuntime.