Create a general purpose stream buffer

MERGE REQUEST

Overview

The viewnode + linkfile MR had a huge new piece of code in it to help the viewnode buffer and fetch data, so that high bitrate data streaming could be supported easily.

This breaks that code out into a separate MR without using any of the code at all. It's not quite ready for use on slower nodes because it doesn't have any adaptive data fetching yet, but this code is ready to be merged.

This architecture will really start to shine once the MDM and stream multiplexers are in place, it was designed to work with them.

Checklist

Review and complete the checklist to ensure that the MR is complete before assigned to an approver.

• All new methods, or updating methods have clear docstrings
• Testing added or updated for new methods
• Any new packages are added to Makefile and .gitlab-ci.yml
• API documentation updated for API updates
• Module README.md updated for changes to work flow
• Issue added to Sia-UI repo for new supporting features
• Changelog updated