Add an option to flush filesystem cache before running?

**Feature request**

This may be useful to get more realistic numbers, instead of zeros when the whole file is within the cache.

**Before submitting**
Please check the following:

- [x] I have described the purpose of the suggested change, specifying what I need the enhancement to accomplish, i.e. what problem it solves.
- [ ] I have included any relevant links, screenshots, environment information, and data relevant to implementing the requested feature, as well as pseudocode for how I want to access the new functionality.
- [ ] If I have ideas for how the new feature could be implemented, I have provided explanations and/or pseudocode and/or task lists for the steps.

Start by locating the Python Jupyter Magic entry point and how measurement options are exposed. Clarify the supported environments and the intended cache-flush behavior before implementation. Done means users can opt into flushing the filesystem cache before a measurement and obtain meaningful non-cached results.

Written by the indexing model from the issue text.