Write automated tests for project buffer save/load

[Moneyl]

Things to test:

• [ ] Repeatedly saving a loading a bunch of non-tiny buffers with known data.
• [ ] Repeatedly read/write tiny buffers without changing size.
• [ ] Repeatedly read/write tiny buffers while changing size to make sure code that moves them into a larger slot works correctly.
• [ ] Perform each step with a known set of data for the buffers. Compare the data read from the buffers with the known data to ensure they're correct.