Establish window checksums

[jakthom]

It would be neat to establish a baseline checksum for time windows, so to ensure/ prove all events made it to all configured destinations between t0 <-> tn.

Good reading on the topic:

• https://sirupsen.com/napkin/problem-14-using-checksums-to-verify
• https://github.com/datafold/data-diff#technical-explanation

Thanks for the suggestion @criccomini!